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<title>User&rsquo;s Guide for TurboVNC 3.0</title>
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<link rel="chapter" href="index.html#hd001" title="1 Legal Information">
<link rel="chapter" href="index.html#hd002" title="2 Conventions Used in This Document">
<link rel="chapter" href="index.html#hd003" title="3 Overview">
<link rel="chapter" href="index.html#hd004" title="4 System Requirements">
<link rel="chapter" href="index.html#hd005" title="5 Obtaining and Installing TurboVNC">
<link rel="chapter" href="index.html#hd006" title="6 Using TurboVNC">
<link rel="chapter" href="index.html#hd007" title="7 Performance and Image Quality">
<link rel="chapter" href="index.html#hd008" title="8 TurboVNC Security Extensions">
<link rel="chapter" href="index.html#hd009" title="9 Hardware 3D Acceleration (Using VirtualGL with TurboVNC)">
<link rel="chapter" href="index.html#hd0010" title="10 Compatibility Guide">
<link rel="chapter" href="index.html#hd0011" title="11 Advanced Configuration">
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<div class="title">
<p class="title">User&rsquo;s Guide for TurboVNC 3.0</p>
</div>
<div id="hd">
<div id="hdBlock" class="hd">
<ul class="hd">
    <li class="Itemize-1 hd">
        <a href="#hd001" class="hd">1 Legal Information</a>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd002" class="hd">2 Conventions Used in This Document</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd002001" class="hd">2.1 Terminology</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd003" class="hd">3 Overview</a>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd004" class="hd">4 System Requirements</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd004001" class="hd">4.1 Linux/x86 and Other x86 Un*x 
                Operating Systems</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd004002" class="hd">4.2 Mac/x86</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd004003" class="hd">4.3 Windows</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd005" class="hd">5 Obtaining and Installing TurboVNC</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd005001" class="hd">5.1 Installing TurboVNC on Linux</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd005002" class="hd">5.2 Installing the TurboVNC Viewer on 
                macOS</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd005003" class="hd">5.3 Installing the TurboVNC Viewer on 
                Windows</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd005004" class="hd">5.4 Installing TurboVNC from Source</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd005005" class="hd">5.5 Uninstalling TurboVNC</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd006" class="hd">6 Using TurboVNC</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd006001" class="hd">6.1 The TurboVNC Session Manager</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006002" class="hd">6.2 Manually Starting a TurboVNC 
                Session</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006003" class="hd">6.3 Manually Connecting to a VNC 
                Server</a>
                <ul class="hd">
                    <li class="Itemize-5 hd">
                        <a href="#hd006003002" class="hd">6.3.2 Window Manager Compatibility</a>
                    </li>
                </ul>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006004" class="hd">6.4 Disconnecting and Killing a TurboVNC 
                Session</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006005" class="hd">6.5 Using TurboVNC in a Web Browser</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006006" class="hd">6.6 Using SSH to Manually Secure a 
                TurboVNC Connection</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006007" class="hd">6.7 Running OpenGL Applications</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd006008" class="hd">6.8 Further Reading</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd007" class="hd">7 Performance and Image Quality</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd007001" class="hd">7.1 Interframe Comparison</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd007002" class="hd">7.2 Advanced Compression Options</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd007003" class="hd">7.3 Lossless Refresh</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd007004" class="hd">7.4 Automatic Lossless Refresh</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd007005" class="hd">7.5 Multithreading</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd008" class="hd">8 TurboVNC Security Extensions</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd008001" class="hd">8.1 Terminology</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd008002" class="hd">8.2 TurboVNC Server Authentication 
                Methods</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd008003" class="hd">8.3 TurboVNC Viewer Authentication 
                Schemes</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd008004" class="hd">8.4 Supported Encryption Methods</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd008005" class="hd">8.5 Supported Security Types</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd008006" class="hd">8.6 Enabling Security Types</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd008007" class="hd">8.7 Further Reading</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd009" class="hd">9 Hardware 3D Acceleration (Using VirtualGL 
        with TurboVNC)</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd009001" class="hd">9.1 Using VirtualGL on a TurboVNC Host</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd009002" class="hd">9.2 Using VirtualGL on a Machine Other 
                Than a TurboVNC Host</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd009003" class="hd">9.3 NV-CONTROL Emulation</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd0010" class="hd">10 Compatibility Guide</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd0010001" class="hd">10.1 TightVNC or TigerVNC Servers</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd0010002" class="hd">10.2 TightVNC or TigerVNC Viewers</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd0010003" class="hd">10.3 RealVNC</a>
            </li>
        </ul>
    </li>
    <li class="Itemize-1 hd">
        <a href="#hd0011" class="hd">11 Advanced Configuration</a>
        <ul class="hd">
            <li class="Itemize-3 hd">
                <a href="#hd0011001" class="hd">11.1 Server Settings</a>
            </li>
            <li class="Itemize-3 hd">
                <a href="#hd0011002" class="hd">11.2 Viewer Settings</a>
            </li>
        </ul>
    </li>
</ul>
</div></div>
<a name="file000"></a>
<p><br /></p>

<hr class="break" />


<h1 id="hd001"><a name="file001"></a>1&nbsp;Legal Information</h1>

<p><img src="somerights20.png" alt="somerights20" class="inline" id="imgid_0" name="imgid_0"/></p>

<p>This document and all associated illustrations are licensed under the 
<span class="remote"><a href="http://creativecommons.org/licenses/by/2.5/" class="remote">Creative 
Commons Attribution 2.5 License</a></span><a name="idx001"></a>.  Any 
works that contain material derived from this document must cite The 
VirtualGL Project as the source of the material and list the current URL 
for the TurboVNC web site.</p>

<p>The official TurboVNC binaries contain libjpeg-turbo, which is based in 
part on the work of the Independent JPEG Group.</p>

<p>TurboVNC is licensed under the <a href="LICENSE.txt">GNU General Public 
License, v2</a><a name="idx002"></a>.</p>

<p><br /></p>

<hr class="break" />



<h1 id="hd002"><a name="file002"></a>2&nbsp;Conventions Used in This Document</h1>

<p>This document assumes that TurboVNC will be installed in the default 
directory (<strong class="filename">/opt/TurboVNC</strong> on Linux/Un*x 
and Mac systems and <strong class="filename">c:\Program 
Files\TurboVNC</strong> on Windows systems.)  If your installation of 
TurboVNC resides in a different directory, then adjust the instructions 
accordingly.</p>


<h2 id="hd002001">2.1&nbsp;Terminology</h2>

<dl class="Description">
    <dt class="Description-1 Description">VNC server (sometimes just &ldquo;server&rdquo;)</dt>
    <dd class="Description-1 Description">
        A computer program, implementing the Remote Framebuffer (RFB) protocol 
        and usually designed to run as a background process, that provides an 
        interactive remote desktop environment through which authenticated users 
        can run graphical programs remotely from other computers on the network.  
        VNC servers can be implemented as single-user screen scrapers, which 
        transmit the contents of the host&rsquo;s physical display (most common 
        with Windows and Mac VNC servers), or as virtual display servers, which 
        provide isolated remote desktop environments for an arbitrary number of 
        simultaneous users on the same host (most common with Un*x VNC servers.)
    </dd>
    <dt class="Description-1 Description">VNC host (sometimes just &ldquo;host&rdquo;)</dt>
    <dd class="Description-1 Description">
        The machine on which a VNC server is running
    </dd>
    <dt class="Description-1 Description">VNC viewer (sometimes just &ldquo;viewer&rdquo;)</dt>
    <dd class="Description-1 Description">
        A computer program, implementing the Remote Framebuffer (RFB) protocol, 
        that connects to a VNC server running on another computer, thus allowing 
        users to run graphical programs remotely.
    </dd>
    <dt class="Description-1 Description">client machine (sometimes just &ldquo;client&rdquo;)</dt>
    <dd class="Description-1 Description">
        The machine on which a VNC viewer is running
    </dd>
    <dt class="Description-1 Description">VNC session (sometimes just &ldquo;session&rdquo;)</dt>
    <dd class="Description-1 Description">
        A specific instance of a Un*x VNC server (Xvnc.)  Each instance of an 
        Xvnc server, including the TurboVNC Server, acts as an independent 
        virtual X server, listening on a unique X11 display number for 
        connections from X11 clients and listening on a unique RFB port number 
        for connections from VNC viewers.  Multiple simultaneous VNC sessions 
        can exist on a given host, under any number of different user accounts.
    </dd>
</dl>

<p><br /></p>

<hr class="break" />



<h1 id="hd003"><a name="file003"></a>3&nbsp;Overview</h1>

<p>TurboVNC is a derivative of VNC (Virtual Network Computing) that is 
tuned to provide peak performance for 3D and video workloads.  TurboVNC 
was originally a fork of 
<span class="remote"><a href="http://www.tightvnc.com" class="remote">TightVNC</a></span><a name="idx003"></a> 
1.3.x, and on the surface, the TurboVNC Server still behaves similarly 
to its parent.  However, the current version of TurboVNC contains a much 
more modern X server code base (based on X.org) and a variety of other 
features and fixes, including a high-performance cross-platform VNC 
viewer.  TurboVNC compresses 3D and video workloads significantly better 
than the &ldquo;tightest&rdquo; compression mode in TightVNC 1.3.x while 
using only typically 15-20% of the CPU time of the latter. Using 
non-default settings, TurboVNC can also match the best compression 
ratios produced by TightVNC 1.3.x for 2D workloads (see Section 
<a href="#AdvancedCompression" class="ref">7.2</a>.)</p>

<p>All VNC implementations, including TurboVNC, use the RFB (remote 
framebuffer) protocol to send &ldquo;framebuffer updates&rdquo; from the 
VNC server to any connected viewers.  Each framebuffer update can 
contain multiple &ldquo;rectangles&rdquo; (regions that have changed 
since the last update.)  As with TightVNC, TurboVNC analyzes each 
rectangle, splits it into multiple &ldquo;subrectangles&rdquo;, and 
attempts to encode each subrectangle using the &ldquo;subencoding 
type&rdquo; that will provide the most efficient compression, given the 
number of unique colors in the subrectangle. The process by which 
TurboVNC does this is referred to as an &ldquo;encoding method.&rdquo; A 
rectangle is first analyzed to determine if any significant portion of 
it is solid, and if so, that portion is encoded as a bounding box and a 
fill color (&ldquo;Solid subencoding.&rdquo;)  Of the remaining 
subrectangles, those with only two colors are encoded as a 
1-bit-per-pixel bitmap with a 2-color palette (&ldquo;Mono 
subencoding&rdquo;), those with low numbers of unique colors are encoded 
as a color palette and an 8-bit-per-pixel bitmap (&ldquo;Indexed color 
subencoding&rdquo;), and subrectangles with high numbers of unique 
colors are encoded using either JPEG or arrays of RGB pixels (&ldquo;Raw 
subencoding&rdquo;), depending on the encoding method. zlib can 
optionally be used to compress the indexed color, mono and raw 
subrectangles.</p>

<p>Part of TurboVNC&rsquo;s speedup comes from the use of libjpeg-turbo, 
the same high-speed SIMD-optimized JPEG codec used by VirtualGL.  
However, TurboVNC also eliminates the CPU-hungry smoothness detection 
routines that TightVNC uses to determine whether a subrectangle is a 
good candidate for JPEG compression, and TurboVNC&rsquo;s encoding 
methods tend to favor the use of JPEG more, since it is now generally 
the fastest subencoding type.  Furthermore, TurboVNC eliminates buffer 
copies, it maximizes network efficiency by splitting framebuffer updates 
into relatively large subrectangles, and it uses only the zlib 
compression levels that can be shown to have a measurable performance 
benefit.</p>

<p>TurboVNC is the product of extensive research, in which many different 
permutations of the TightVNC encoder were benchmarked at the low level 
against a variety of RFB session captures that simulate real-world 
application workloads, both 2D and 3D.  For more information on the 
research leading to TurboVNC&rsquo;s encoder design, see 
<span class="remote"><a href="http://www.TurboVNC.org/pmwiki/uploads/About/tighttoturbo.pdf" class="remote">this 
report</a></span><a name="idx004"></a>.</p>

<p>In addition to high performance, other notable features of TurboVNC 
include:</p>

<ul class="Itemize">
    <li class="Itemize-1 Itemize asterisk">
        Fine-grained control over the JPEG image quality and the level of 
        chrominance subsampling
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Double buffering on the client side to reduce tearing artifacts in 3D 
        and video applications
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Flexible and configurable full-screen/multi-screen support
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Full support for IPv6
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Advanced flow control and continuous updates.  This allows viewers to 
        receive framebuffer updates without specifically requesting them, which 
        can improve performance dramatically on high-latency connections.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Authentication with one-time passwords or Unix login credentials.  
        Access control lists can be used to share TurboVNC sessions with only 
        certain users.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Built-in SSH client (part of the TurboVNC Viewer) that supports OpenSSH 
        config files and password-less public key authentication (using 
        ssh-agent or Pageant)
    </li>
    <li class="Itemize-1 Itemize asterisk">
        The TurboVNC Session Manager (part of the TurboVNC Viewer) allows users 
        to interactively choose a TurboVNC session to which to connect, as well 
        as to remotely start and kill TurboVNC sessions.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TLS encryption support (VeNCrypt-compatible)
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC allows security/authentication policies to be set globally for 
        a particular host.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Multithreaded Tight encoding
    </li>
    <li class="Itemize-1 Itemize asterisk">
        &ldquo;Lossless refresh&rdquo; allows a viewer to request a lossless 
        copy of the current screen image.  This is useful in situations in which 
        image quality is critical but the network is too slow to support sending 
        a high-quality image for every frame.  Lossless refreshes can be 
        performed manually when a certain hotkey is pressed, or the TurboVNC 
        Server can be configured to send a lossless refresh automatically if the 
        user stops interacting with the application for a certain period of time.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        High-performance feature-rich VNC viewer
    </li>
    <li class="Itemize-1 Itemize asterisk">
        The TurboVNC Server integrates with 
        <span class="remote"><a href="https://novnc.com" class="remote">noVNC</a></span><a name="idx005"></a> 
        to provide a zero-install viewer for TurboVNC sessions that works in any 
        web browser (with reduced performance and features relative to the 
        TurboVNC Viewer)
    </li>
    <li class="Itemize-1 Itemize asterisk">
        The TurboVNC Server and TurboVNC Viewer can be used with an instance of 
        the UltraVNC Repeater in Mode I or II.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Remote extended input device support
    </li>
</ul>

<p>TurboVNC, when used with VirtualGL, provides a highly performant and 
robust solution for remotely displaying 3D applications over all types 
of networks.</p>

<p>On &ldquo;modern&rdquo; hardware, TurboVNC is capable of streaming 50+ 
Megapixels/second over a 100 Megabit/second local area network with 
perceptually lossless image quality.  TurboVNC can stream between 10 and 
12 Megapixels/second over a 5 Megabit/second broadband connection at 
reduced (but usable) image quality.</p>

<p>TurboVNC is compatible with other VNC distributions.  See Chapter 
<a href="#Compatibility" class="ref">10</a> for more information.  The 
official TurboVNC binaries can be installed onto the same system as 
other VNC distributions without interference.</p>

<p><br /></p>

<hr class="break" />



<h1 id="hd004"><a name="file004"></a>4&nbsp;System Requirements</h1>


<h2 id="hd004001">4.1&nbsp;Linux/x86 and Other x86 Un*x Operating Systems</h2>

<div class="table">
<table class="standard">
  <thead class="standard">
  <tr class="head ">
    <th class="head standard"></th>
    <th class="head standard">Host (x86)</th>
    <th class="head standard">Host (x86-64)</th>
    <th class="head standard">Client (x86 or non-Linux)</th>
    <th class="head standard">Client (Linux/x86-64)</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="high standard">Recommended CPU</td>
    <td class="standard"><ul class="Itemize"><li class="Itemize-0">
    For optimal performance, the CPU should support SSE2 extensions.
</li>
<li class="Itemize-0">
    Dual processors or dual cores recommended
</li></ul></td>
    <td class="standard">Dual processors or dual cores recommended</td>
    <td class="standard">For optimal performance, the CPU should support SSE2 extensions.</td>
    <td class="standard"></td>
  </tr>
  <tr class="standard">
    <td class="high standard">O/S</td>
    <td class="standard" colspan="4">TurboVNC should work with a variety of Linux distributions, <span class="remote"><a href="http://www.freebsd.org" class="remote">FreeBSD</a></span><a name="idx006"></a>, and <span class="remote"><a href="http://www.oracle.com/us/products/servers-storage/solaris" class="remote">Solaris</a></span><a name="idx007"></a>, but currently-supported versions of <span class="remote"><a href="http://www.redhat.com/products/enterprise-linux/" class="remote">Red Hat Enterprise Linux</a></span><a name="idx008"></a> (and its work-alikes, including <span class="remote"><a href="http://www.centos.org" class="remote">CentOS</a></span><a name="idx009"></a>, <span class="remote"><a href="http://www.oracle.com/us/technologies/linux" class="remote">Oracle Linux</a></span><a name="idx0010"></a>, and <span class="remote"><a href="https://www.scientificlinux.org" class="remote">Scientific Linux</a></span><a name="idx0011"></a>), <span class="remote"><a href="http://www.ubuntu.com" class="remote">Ubuntu</a></span><a name="idx0012"></a> LTS, and <span class="remote"><a href="http://www.suse.com" class="remote">SuSE</a></span><a name="idx0013"></a> Linux Enterprise tend to receive the most attention from the TurboVNC community.</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Other</td>
    <td class="standard" colspan="2">SSH server (if using the <a href="#TurboVNC_Session_Manager">TurboVNC Session Manager</a><a name="idx0014"></a>)</td>
    <td class="standard"><ul class="Itemize"><li class="Itemize-0">
    For optimal performance, the X server should be configured to export 
    True Color (24-bit or 32-bit) visuals.
</li>
<li class="Itemize-0">
    <span class="remote"><a href="http://www.java.com" class="remote">Oracle 
    Java</a></span><a name="idx0015"></a> or OpenJDK
</li></ul></td>
    <td class="standard">For optimal performance, the X server should be configured to export True Color (24-bit or 32-bit) visuals.</td>
  </tr>
</table>
</div>




<h2 id="hd004002">4.2&nbsp;Mac/x86</h2>

<div class="table">
<table class="standard">
  <thead class="standard">
  <tr class="head ">
    <th class="head standard"></th>
    <th class="head standard">Client</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="high standard">Recommended CPU</td>
    <td class="standard">Any 64-bit Intel-based Mac</td>
  </tr>
  <tr class="standard">
    <td class="high standard">O/S</td>
    <td class="standard">OS X/macOS 10.10 &ldquo;Yosemite&rdquo; or later</td>
  </tr>
</table>
</div>




<h2 id="hd004003">4.3&nbsp;Windows</h2>

<div class="table">
<table class="standard">
  <thead class="standard">
  <tr class="head ">
    <th class="head standard"></th>
    <th class="head standard">Client</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="high standard">Recommended CPU</td>
    <td class="standard">For optimal performance, the CPU should support SSE2 extensions.</td>
  </tr>
  <tr class="standard">
    <td class="high standard">O/S</td>
    <td class="standard">Windows 7 or later</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Other</td>
    <td class="standard">For optimal performance, the client display should have a 24-bit or 32-bit (True Color) color depth.</td>
  </tr>
</table>
</div>


<p><br /></p>

<hr class="break" />



<h1 id="hd005"><a name="file005"></a>5&nbsp;Obtaining and Installing TurboVNC</h1>


<h2 id="hd005001">5.1&nbsp;Installing TurboVNC on Linux</h2>


<h3 id="hd005001001">Installing TurboVNC</h3>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered" value="1">
        Download the appropriate TurboVNC binary package for your system from 
        the 
        <span class="remote"><a href="http://sourceforge.net/projects/turbovnc/files/" class="remote">Files 
        area</a></span><a name="idx0016"></a> of the 
        <span class="remote"><a href="http://sourceforge.net/projects/turbovnc" class="remote">TurboVNC 
        SourceForge project page</a></span><a name="idx0017"></a>. Packages are 
        provided for RPM-based and Debian-based Linux distributions that contain 
        GLIBC 2.12 or later. <br />
    </li>
    <li class="Ordered-1 Ordered" value="2">
        cd to the directory where you downloaded the binary package, and issue 
        one of the following commands as root:
        <dl class="Description">
            <dt class="Description-3 Description">RPM-based systems using YUM</dt>
            <dd class="Description-3 Description">
<pre class="verbatim">
yum&nbsp;install&nbsp;turbovnc*.rpm
</pre>

            </dd>
            <dt class="Description-3 Description">RPM-based systems using DNF</dt>
            <dd class="Description-3 Description">
<pre class="verbatim">
dnf&nbsp;install&nbsp;turbovnc*.rpm
</pre>

            </dd>
            <dt class="Description-3 Description">RPM-based systems using YaST2</dt>
            <dd class="Description-3 Description">
<pre class="verbatim">
yast2&nbsp;--install&nbsp;turbovnc*.rpm
</pre>

            </dd>
            <dt class="Description-3 Description">Other RPM-based systems (dependencies will not be installed automatically)</dt>
            <dd class="Description-3 Description">
<pre class="verbatim">
rpm&nbsp;-U&nbsp;turbovnc*.rpm
</pre>

            </dd>
            <dt class="Description-3 Description">Debian-based systems</dt>
            <dd class="Description-3 Description">
<pre class="verbatim">
dpkg&nbsp;-i&nbsp;turbovnc*.deb
apt&nbsp;install&nbsp;-f
</pre>

            </dd>
        </dl>
    </li>
</ol>



<h3 id="hd005001002">Installing TurboVNC for a Single User</h3>

<p>Download the appropriate binary package, as above, then execute the 
following commands:</p>

<dl class="Description">
    <dt class="Description-1 Description">RPM-based systems</dt>
    <dd class="Description-1 Description">
        <pre class="verbatim">mkdir ~/turbovnc<br />cd ~/turbovnc<br />rpm2cpio <em>full/path/of/turbovnc*.rpm</em> | cpio -idv</pre>
    </dd>
    <dt class="Description-1 Description">Debian-based systems</dt>
    <dd class="Description-1 Description">
        <pre class="verbatim">dpkg-deb &ndash;extract <em>full/path/of/turbovnc*.deb</em> ~/turbovnc</pre>
    </dd>
</dl>

<p>Add <strong class="filename">~/turbovnc</strong> to any paths specified 
in this document.</p>

<div class="important"><p class="important">
If using the TurboVNC Session Manager, set the <code>turbovnc.serverdir</code> Java system property in the TurboVNC Viewer to <code>~/turbovnc/opt/TurboVNC</code>, or set the <code>TVNC_SERVERDIR</code> environment variable on the client machine to <code>\~/turbovnc/opt/TurboVNC</code> (note backslash.)  Refer to Section <a href="#TVNC_SERVERDIR" class="ref">11.2</a>.
</p></div>

<div class="important"><p class="important">
The TurboVNC security configuration file will not work when TurboVNC is installed in this manner.
</p></div>



<h2 id="hd005002">5.2&nbsp;Installing the TurboVNC Viewer on macOS</h2>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered">
        Download the TurboVNC Mac disk image 
        (<strong class="filename">TurboVNC-2.2.80.dmg</strong>) from the 
        <span class="remote"><a href="http://sourceforge.net/projects/turbovnc/files/" class="remote">Files 
        area</a></span><a name="idx0018"></a> of the 
        <span class="remote"><a href="http://sourceforge.net/projects/turbovnc" class="remote">TurboVNC 
        SourceForge project page</a></span><a name="idx0019"></a>.
    </li>
    <li class="Ordered-1 Ordered">
        Open the disk image, then open 
        <strong class="filename">TurboVNC.pkg</strong> inside the disk image. 
        Follow the instructions to install the Mac TurboVNC Viewer.
    </li>
</ol>



<h2 id="hd005003">5.3&nbsp;Installing the TurboVNC Viewer on Windows</h2>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered">
        Download the TurboVNC Windows installer package 
        (<strong class="filename">TurboVNC-2.2.80-x64.exe</strong> for 64-bit 
        systems or <strong class="filename">TurboVNC-2.2.80-x86.exe</strong> for 
        legacy 32-bit-only systems) from the 
        <span class="remote"><a href="http://sourceforge.net/projects/turbovnc/files/" class="remote">Files 
        area</a></span><a name="idx0020"></a> of the 
        <span class="remote"><a href="http://sourceforge.net/projects/turbovnc" class="remote">TurboVNC 
        SourceForge project page</a></span><a name="idx0021"></a>.
    </li>
    <li class="Ordered-1 Ordered">
        Run the TurboVNC installer.  The installation of TurboVNC should be 
        self-explanatory.  The only configuration option is the directory into 
        which you want the files to be installed.
    </li>
</ol>



<h2 id="hd005004">5.4&nbsp;Installing TurboVNC from Source</h2>

<p>If you are using a Linux/Un*x platform for which there is not a 
pre-built TurboVNC binary package available, then download the TurboVNC 
source tarball 
(<strong class="filename">turbovnc-2.2.80.tar.gz</strong>) from the 
<span class="remote"><a href="http://sourceforge.net/projects/turbovnc/files/" class="remote">Files 
area</a></span><a name="idx0022"></a> of the 
<span class="remote"><a href="http://sourceforge.net/projects/turbovnc" class="remote">TurboVNC 
SourceForge project page</a></span><a name="idx0023"></a>, uncompress 
it, <code>cd turbovnc-2.2.80</code>, and read 
<strong class="filename">BUILDING.md</strong> for further instructions 
on how to build TurboVNC from source.</p>



<h2 id="hd005005">5.5&nbsp;Uninstalling TurboVNC</h2>


<h3 id="hd005005001">Linux</h3>

<p>As root, issue one of the following commands:</p>

<dl class="Description">
    <dt class="Description-1 Description">RPM-based systems</dt>
    <dd class="Description-1 Description">
<pre class="verbatim">
rpm&nbsp;-e&nbsp;turbovnc
</pre>

    </dd>
    <dt class="Description-1 Description">Debian-based systems</dt>
    <dd class="Description-1 Description">
<pre class="verbatim">
dpkg&nbsp;-r&nbsp;turbovnc
</pre>

    </dd>
</dl>



<h3 id="hd005005002">macOS</h3>

<p>Open the <strong class="filename">Uninstall TurboVNC</strong> 
application, located in the <strong class="filename">TurboVNC</strong> 
Applications folder.  You can also open a terminal and execute:</p>

<pre class="verbatim">
sudo&nbsp;/opt/TurboVNC/bin/uninstall
</pre>



<h3 id="hd005005003">Windows</h3>

<p>Use the <strong class="filename">Programs and Features</strong> applet 
in the Control Panel (or the <strong class="filename">Apps &amp; 
Features</strong> applet if you are running Windows 10), or select 
<strong class="filename">Uninstall TurboVNC</strong> in the 
<strong class="filename">TurboVNC</strong> Start Menu group.</p>

<p><br /></p>

<hr class="break" />



<h1 id="hd006"><a name="file006"></a>6&nbsp;Using TurboVNC</h1>

<p><a name="TurboVNC_Usage"></a></p>


<h2 id="hd006001">6.1&nbsp;The TurboVNC Session Manager</h2>

<p><a name="TurboVNC_Session_Manager"></a></p>

<p>The TurboVNC Viewer, like any VNC viewer, can be used to connect to any 
VNC server.  However, the TurboVNC Viewer also includes the TurboVNC 
Session Manager, which can be used with the TurboVNC Server to remotely 
start or kill a TurboVNC session, list all TurboVNC sessions running 
under a particular user account on a particular host, and choose a 
TurboVNC session to which to connect.  The TurboVNC Session Manager uses 
the TurboVNC Viewer&rsquo;s built-in SSH client, which supports OpenSSH 
config files and password-less public key authentication (using 
ssh-agent or Pageant.)</p>


<h3 id="hd006001001">Procedure</h3>

<ul class="Itemize">
    <li class="Itemize-1 Itemize asterisk">
        On the client machine, start the TurboVNC Viewer.
        <dl class="Description">
            <dt class="Description-3 Description">Linux/Un*x clients</dt>
            <dd class="Description-3 Description">
                 Open a new terminal/xterm and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>

            </dd>
            <dt class="Description-3 Description">Mac clients</dt>
            <dd class="Description-3 Description">
                 Open the <strong class="filename">TurboVNC Viewer</strong> application, 
                 located in the <strong class="filename">TurboVNC</strong> Applications 
                 folder, or open a new terminal and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>

            </dd>
            <dt class="Description-3 Description">Windows clients</dt>
            <dd class="Description-3 Description">
                 Select <strong class="filename">TurboVNC Viewer</strong> in the 
                 <strong class="filename">TurboVNC</strong> Start Menu group, or open a 
                 new command prompt and type
<pre class="verbatim">
c:\Program&nbsp;Files\TurboVNC\vncviewer.bat
</pre>

            </dd>
        </dl>
    </li>
    <li class="Itemize-1 Itemize asterisk">
        A small dialog box will appear. <br /><br /> 
        <img src="newconn-sessmgr.png" alt="newconn-sessmgr" class="inline" id="imgid_1" name="imgid_1"/> 
        <br /><br /> Enter the hostname or IP address of the TurboVNC host in 
        the &ldquo;VNC server&rdquo; field, then click &ldquo;Connect&rdquo;. 
        <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        The TurboVNC Session Manager will connect to the host using SSH, and it 
        will prompt for an SSH private key passphrase or an SSH password, if 
        necessary.  (The TurboVNC Viewer&rsquo;s built-in SSH client will first 
        try to fetch the private key passphrase from ssh-agent or Pageant, if 
        either is running.)
        <div class="important"><p class="important">
        You can specify the SSH username, if it differs from your local username, by prefixing the hostname/IP address with <code><em>user</em>@</code>, where <em><code>user</code></em> is the SSH username.
        </p></div>
    </li>
    <li class="Itemize-1 Itemize asterisk">
        If no TurboVNC sessions are currently running under your user account on 
        the TurboVNC host, then the session manager will: <br /><br />
        <ul class="Itemize">
            <li class="Itemize-3 Itemize asterisk">
                start a new session
            </li>
            <li class="Itemize-3 Itemize asterisk">
                generate a new one-time password (OTP) for the session
            </li>
            <li class="Itemize-3 Itemize asterisk">
                automatically configure the TurboVNC Viewer so that it tunnels the VNC 
                connection through SSH (reusing the SSH channel that the session manager 
                already opened) and authenticates with the newly-generated OTP
            </li>
            <li class="Itemize-3 Itemize asterisk">
                connect to the session
            </li>
        </ul>
        <br class="itempara" />Once connected, a TurboVNC desktop window should appear on your client 
        machine.  This window contains a virtual desktop with which you can 
        interact to launch X-Windows applications on the TurboVNC host. 
        <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        If one or more TurboVNC sessions are currently running under your user 
        account on the TurboVNC host, then the session manager will enumerate 
        the sessions and display a dialog similar to the following, allowing you 
        to manage the sessions remotely, to start a new session, or to choose a 
        session to which to connect: <br /><br /> 
        <img src="sessmgr.png" alt="sessmgr" class="inline" id="imgid_2" name="imgid_2"/> 
        <br /><br /> Upon choosing a session to which to connect, the session 
        manager will (as described above) automatically generate a new OTP for 
        the session and configure the TurboVNC Viewer so that it tunnels the VNC 
        connection through SSH and authenticates with the newly-generated OTP. 
        <br /><br /> One-time passwords can be used with any VNC viewer, so 
        generating a new OTP for a TurboVNC session (using the &ldquo;New 
        OTP&rdquo; button) is a convenient way of allowing colleagues to 
        temporarily access the session.  Generating a new OTP for a TurboVNC 
        session is also useful when using 
        <a href="#noVNC">noVNC</a><a name="idx0024"></a>.  If 
        &ldquo;View-only&rdquo; is checked, then users who authenticate with the 
        new OTP will not be able to remotely control the session.
        <div class="important"><p class="important">
        The TurboVNC Session Manager automatically uses SSH tunneling and OTP authentication by default, but you can pass <code>-nosessmgrauto</code> on the TurboVNC Viewer command line to disable this behavior, thus allowing any authentication/encryption method to be used.  Additional command-line parameters can be used to specify the port on which the SSH server is listening and the location of the SSH private key file.  The OpenSSH config file (<strong class="filename">~/.ssh/config</strong> by default) can also be used to specify those parameters persistently for a given host.
        </p></div>
        <div class="important"><p class="important">
        The <code>TVNC_SERVERDIR</code> and <code>TVNC_SERVERARGS</code> environment variables, and their equivalent Java system properties (<code>turbovnc.serverdir</code> and <code>turbovnc.serverargs</code>) can be used to specify a non-default installation path for the TurboVNC Server or additional arguments to pass to the TurboVNC Server when starting new sessions (refer to Section <a href="#TVNC_SERVERARGS" class="ref">11.2</a>.)  These arguments can also be specified on the server using the system-wide or per-user <strong class="filename">turbovncserver.conf</strong> file.
        </p></div>
    </li>
</ul>



<h2 id="hd006002">6.2&nbsp;Manually Starting a TurboVNC Session</h2>


<h3 id="hd006002001">Procedure</h3>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered">
        Open a new Command Prompt/terminal window on your client machine.
    </li>
    <li class="Ordered-1 Ordered">
        In the new Command Prompt/terminal window, open a Secure Shell (SSH) 
        session into the TurboVNC host:
        <pre class="verbatim">ssh <em>user</em>@<em>host</em></pre>
        Replace <em><code>user</code></em> with your username on the TurboVNC 
        host and <em><code>host</code></em> with the hostname or IP address of 
        the host.
    </li>
    <li class="Ordered-1 Ordered">
        In the SSH session, start a TurboVNC session:
<pre class="verbatim">
/opt/TurboVNC/bin/vncserver
</pre>

    </li>
    <li class="Ordered-1 Ordered">
        Make a note of the X display number that the TurboVNC session is 
        occupying, for instance: <br /><br /> 
        <code>Desktop&nbsp;'TurboVNC:&nbsp;my_host:1&nbsp;(my_user)'&nbsp;started&nbsp;on&nbsp;display&nbsp;my_host:1</code> 
        <br /><br /> If this is the first time that a TurboVNC session has ever 
        been run under this user account, and if VNC password authentication is 
        enabled for the session, then TurboVNC will prompt for a VNC password.
    </li>
    <li class="Ordered-1 Ordered">
        The SSH session can now be exited, if desired.
    </li>
</ol>



<h2 id="hd006003">6.3&nbsp;Manually Connecting to a VNC Server</h2>


<h3 id="hd006003001">Procedure</h3>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered">
        On the client machine, start the TurboVNC Viewer.
        <dl class="Description">
            <dt class="Description-3 Description">Linux/Un*x clients</dt>
            <dd class="Description-3 Description">
                 Open a new terminal/xterm and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>

            </dd>
            <dt class="Description-3 Description">Mac clients</dt>
            <dd class="Description-3 Description">
                 Open the <strong class="filename">TurboVNC Viewer</strong> application, 
                 located in the <strong class="filename">TurboVNC</strong> Applications 
                 folder, or open a new terminal and type
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer
</pre>

            </dd>
            <dt class="Description-3 Description">Windows clients</dt>
            <dd class="Description-3 Description">
                 Select <strong class="filename">TurboVNC Viewer</strong> in the 
                 <strong class="filename">TurboVNC</strong> Start Menu group, or open a 
                 new command prompt and type
<pre class="verbatim">
c:\Program&nbsp;Files\TurboVNC\vncviewer.bat
</pre>

            </dd>
        </dl>
    </li>
    <li class="Ordered-1 Ordered">
        A small dialog box will appear. <br /><br /> 
        <img src="newconn.png" alt="newconn" class="inline" id="imgid_3" name="imgid_3"/> 
        <br /><br /> Enter the X display name (hostname, or IP address, and 
        display number) of the VNC server or TurboVNC session in the &ldquo;VNC 
        server&rdquo; field, then click &ldquo;Connect&rdquo;.
    </li>
    <li class="Ordered-1 Ordered">
        Another dialog box appears, prompting for the password (if Standard VNC 
        authentication is being used) or for the username and password (if Unix 
        Login authentication is being used.) <br /><br />
        <div class="table">
        <table class="standard">
          <tr class="standard">
            <td class="standard">Standard VNC Authentication Dialog</td>
            <td class="standard"><img src="vncauth.png" alt="vncauth" class="inline" id="imgid_4" name="imgid_4"/></td>
          </tr>
          <tr class="standard">
            <td class="standard">Unix Login Authentication Dialog</td>
            <td class="standard"><img src="unixauth.png" alt="unixauth" class="inline" id="imgid_5" name="imgid_5"/></td>
          </tr>
        </table>
        </div>
        
        <br /> Enter the VNC server password or the Unix username/password and 
        press Enter. <br /><br /> A VNC desktop window should appear on your 
        client machine.  This window contains a virtual desktop with which you 
        can interact to launch graphical applications on the VNC host.
        <div class="important"><p class="important">
        If you are connecting to a non-VeNCrypt-compatible VNC server, then the authentication dialog will warn you that the connection is not encrypted: <br /><br /> <img src="vncauth-insecure.png" alt="vncauth-insecure" class="inline" id="imgid_6" name="imgid_6"/> <br /><br /> You should never use Unix Login authentication with an unencrypted connection.  Instead, tunnel the connection through SSH (see Section <a href="#Secure_TurboVNC_Usage" class="ref">6.6</a> below for more details.)
        </p></div>
    </li>
</ol>



<h3 id="hd006003002">6.3.2&nbsp;Window Manager Compatibility</h3>

<p>This version of the TurboVNC Server can run 3D (compositing) window 
managers (such as Unity or GNOME 3+ or KDE 5+) using its built-in 
software OpenGL implementation, and it also provides an option 
(<code>-vgl</code>) that allows for running 3D window managers using 
VirtualGL.  However, for performance reasons, it is generally 
recommended that you use a 2D window manager with the TurboVNC Server 
(even with VirtualGL, 3D window managers have a lot of overhead.)  As of 
this writing, Ubuntu, RHEL 7+, and Fedora provide an optional 2D window 
manager called &ldquo;GNOME Fallback&rdquo;, &ldquo;GNOME 
Flashback&rdquo;, or &ldquo;GNOME Classic&rdquo;, which will 
automatically be used if it is installed and the <code>TVNC_WM</code> 
environment variable is set to <code>2d</code>.  For other systems that 
lack a 2D window manager, it is recommended that you install MATE.  
Refer to 
<span class="remote"><a href="http://www.turbovnc.org/Documentation/Compatibility30" class="remote">this 
report</a></span><a name="idx0025"></a> for an up-to-date list of window 
managers that have been tested with this version of the TurboVNC Server, 
how to configure the TurboVNC Server to use those window managers, and a 
list of known compatibility issues.</p>



<h2 id="hd006004">6.4&nbsp;Disconnecting and Killing a TurboVNC Session</h2>

<p>Closing the TurboVNC Viewer disconnects from the TurboVNC session, but 
the TurboVNC session will remain running on the TurboVNC host (as will 
any applications that you may have started within the session), and you 
can reconnect to the session at any time.</p>

<p>If the TurboVNC session was created with default settings, then the 
easiest way to kill it is to log out of the window manager running in 
the session.  You can also use the 
<a href="#TurboVNC_Session_Manager">TurboVNC Session 
Manager</a><a name="idx0026"></a> to remotely kill TurboVNC sessions, or 
you can type the following command:</p>

<pre class="verbatim">/opt/TurboVNC/bin/vncserver -kill :<em>n</em></pre>
<p>from a terminal in the TurboVNC session or from an SSH session on the 
host. Replace <em><code>n</code></em> with the X display number of the 
TurboVNC session you want to kill.</p>

<p>To list the X display numbers and process ID&rsquo;s of all TurboVNC 
sessions currently running under your user account on a particular host, 
type the following command:</p>

<pre class="verbatim">
/opt/TurboVNC/bin/vncserver&nbsp;-list
</pre>

<p>from a terminal in the TurboVNC session or from an SSH session on the 
host.</p>



<h2 id="hd006005">6.5&nbsp;Using TurboVNC in a Web Browser</h2>

<p><a name="noVNC"></a></p>

<p>When a TurboVNC session is started, the <code>vncserver</code> script 
can optionally start a simple web server that serves up 
<span class="remote"><a href="https://novnc.com" class="remote">noVNC</a></span><a name="idx0027"></a>, 
an HTML 5/JavaScript VNC viewer that works in any web browser (with 
reduced performance and features relative to the TurboVNC Viewer.)  This 
allows you to easily connect to a TurboVNC session from a machine that 
does not have the TurboVNC Viewer installed (including mobile devices.)</p>

<p>To launch noVNC along with a TurboVNC session, pass <code>-novnc 
<em>dir</em></code> to <code>/opt/TurboVNC/bin/vncserver</code> when 
starting the session, where <em><code>dir</code></em> is the directory 
containing noVNC (setting the <code>$noVNC</code> variable in 
<strong class="filename">turbovncserver.conf</strong> has the same 
effect.)  The <code>vncserver</code> script will print the noVNC URL, 
which will be of the form:</p>

<pre class="verbatim">http://<em>host</em>:<em>5800+n</em>/vnc.html?host=<em>host</em>&amp;port=<em>5900+n</em></pre>
<p>or</p>

<pre class="verbatim">https://<em>host</em>:<em>5800+n</em>/vnc.html?host=<em>host</em>&amp;port=<em>5900+n</em>&amp;encrypt=1</pre>
<p>where <em><code>host</code></em> is the hostname or IP address of the 
TurboVNC host, and <em><code>n</code></em> is the X display number of 
the TurboVNC session.</p>

<p>Point your web browser to that URL in order to access the TurboVNC 
session. You can optionally pass <code>-x509cert 
<em>certificate-file</em> -x509key <em>private-key-file</em></code> to 
<code>vncserver</code> to encrypt both the HTTP and RFB connections.  
See the <code>vncserver</code> man page for more details.</p>

<div class="important"><p class="important">
NOTE: noVNC only supports VNC Password authentication, so it is strongly recommended that it be used only with one-time passwords unless the connections are encrypted.
</p></div>



<h2 id="hd006006">6.6&nbsp;Using SSH to Manually Secure a TurboVNC Connection</h2>

<p><a name="Secure_TurboVNC_Usage"></a></p>

<p>If the <a href="#TurboVNC_Session_Manager">TurboVNC Session 
Manager</a><a name="idx0028"></a> is not being used, then the connection 
between the TurboVNC Server and the TurboVNC Viewer will, by default, 
use Anonymous TLS encryption (refer to Chapter 
<a href="#Security_Extensions" class="ref">8</a>.)  However, it may be 
preferable to secure the TurboVNC connection using SSH rather than 
Anonymous TLS encryption, particularly if one does not want to open 
additional ports in the host&rsquo;s firewall.  This can easily be 
accomplished by using the <code>-via</code> and <code>-tunnel</code> 
command-line options in the TurboVNC Viewer (or the equivalent GUI 
options, which are located under the &ldquo;Security&rdquo; tab in the 
Options dialog.)</p>

<p>The <code>-via</code> and <code>-tunnel</code> options in the TurboVNC 
Viewer take advantage of the port forwarding feature in SSH.  For 
instance, running</p>

<pre class="verbatim"><em>vncviewer</em> -via <em>user</em>@<em>host</em> localhost:<em>n</em></pre>
<p>or</p>

<pre class="verbatim"><em>vncviewer</em> -tunnel <em>user</em>@<em>host</em></pre>
<p>is the equivalent of running</p>

<pre class="verbatim">ssh -L <em>fp</em>:localhost:<em>5900+n</em> <em>user</em>@<em>host</em>
<em>vncviewer</em> localhost::<em>fp</em></pre>
<p>where <em><code>fp</code></em> is a free TCP port on the client machine 
(this is automatically determined by the TurboVNC Viewer.)</p>

<div class="important"><p class="important">
In the above examples, <em><code>vncviewer</code></em> is the command used to launch the TurboVNC Viewer&ndash; <code>/opt/TurboVNC/bin/vncviewer</code> on Mac/Linux/Un*x systems or <code>c:\Program&nbsp;Files\TurboVNC\vncviewer.bat</code> on Windows systems.
</p></div>

<p><code>-tunnel</code> can be used as a shortcut whenever the SSH and VNC 
hosts are the same machine.  <code>-via</code> is more flexible, since 
it allows you to specify the VNC server to which to connect.  The VNC 
server is specified from the point of view of the SSH server, which is 
why we used <code>localhost</code> in the above example.</p>

<p>The command used to establish the SSH tunnel is configurable by way of 
environment variables.  See Section 
<a href="#VNC_VIA_CMD" class="ref">11.2</a> for more details.</p>


<h3 id="hd006006001">Forcing SSH Connections</h3>

<p>Passing an argument of <code>-localhost</code> to <code>vncserver</code> 
will force the TurboVNC session to accept inbound connections only from 
the TurboVNC host.  This effectively forces SSH tunneling to be used for 
remote connections.  If the <code>no-remote-connections</code> directive 
is set in the TurboVNC security configuration file, then that has the 
effect of enabling the <code>-localhost</code> option for all new 
TurboVNC sessions that are started on the host.</p>

<p>Passing an argument of <code>-noreverse</code> to <code>vncserver</code> 
will disable the ability to make outbound (reverse) connections from the 
TurboVNC session.  If the <code>no-reverse-connections</code> directive 
is set in the TurboVNC security configuration file, then that has the 
effect of enabling the <code>-noreverse</code> option for all new 
TurboVNC sessions that are started on the host.</p>

<p>If the host is configured such that it only allows SSH connections, then 
disallowing the TLS* security types on a system-wide basis (by setting 
the <code>permitted-security-types</code> directive in the TurboVNC 
security configuration file) is recommended.  Otherwise, when using the 
TurboVNC Viewer with default settings, the connection will have 
redundant encryption.</p>

<p><img src="vncauth-redundant.png" alt="vncauth-redundant" class="inline" id="imgid_7" name="imgid_7"/></p>



<h2 id="hd006007">6.7&nbsp;Running OpenGL Applications</h2>

<p>The TurboVNC Server includes a software GLX/OpenGL implementation that 
can be used for casual 3D rendering.  This implementation uses the 
swrast DRI driver provided by Mesa 8.x and later, and it supports only 
direct rendering.  Thus, it can only be used on systems that do not have 
vendor-specific GPU drivers installed or on systems that provide a 
libglvnd-enabled build of Mesa.  In general, if the TurboVNC host has a 
GPU, then you should use 
<a href="#VGL">VirtualGL</a><a name="idx0029"></a> rather than relying 
on TurboVNC&rsquo;s software OpenGL implementation.</p>

<p>Passing <code>-extension&nbsp;GLX</code> to <code>vncserver</code> 
disables the built-in GLX/OpenGL implementation, thus restoring the 
behavior of TurboVNC 2.1.x and earlier (which required VirtualGL in 
order to run OpenGL applications.)  If the built-in GLX/OpenGL 
implementation is not functioning properly, then pass 
<code>-verbose</code> to <code>vncserver</code> to log informational 
messages that may reveal the source of the problem.</p>



<h2 id="hd006008">6.8&nbsp;Further Reading</h2>

<p>For more detailed instructions on the usage of TurboVNC:</p>

<dl class="Description">
    <dt class="Description-1 Description">TurboVNC Server</dt>
    <dd class="Description-1 Description">
        Refer to the TurboVNC man pages:
<pre class="verbatim">
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;vncserver
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;Xvnc
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;vncconnect
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;vncpasswd
</pre>

    </dd>
    <dt class="Description-1 Description">TurboVNC Viewer</dt>
    <dd class="Description-1 Description">
        Run
<pre class="verbatim">
/opt/TurboVNC/bin/vncviewer&nbsp;-?
</pre>

        on Un*x or
<pre class="verbatim">
c:\Program&nbsp;Files\TurboVNC\vncviewer.bat&nbsp;-?
</pre>

        on Windows to display a full list of supported command-line 
        options/parameters and their descriptions.
    </dd>
</dl>

<p><br /></p>

<hr class="break" />



<h1 id="hd007"><a name="file007"></a>7&nbsp;Performance and Image Quality</h1>

<p>The level of image compression in TurboVNC can be adjusted to balance 
the (sometimes conflicting) goals of high image quality and high 
performance. There are four options that control the manner in which 
TurboVNC compresses images:</p>

<dl class="Description">
    <dt class="Description-1 Description">Allow JPEG compression</dt>
    <dd class="Description-1 Description">
         If this option is enabled, then TurboVNC will use JPEG compression for 
         subrectangles that have a high number of unique colors, and it will use 
         indexed color subencoding for subrectangles that have a low number of 
         unique colors.  If this option is disabled, then TurboVNC will select 
         between indexed color or raw subencoding, depending on the size of the 
         subrectangle and its color count.
    </dd>
    <dt class="Description-1 Description">JPEG image quality</dt>
    <dd class="Description-1 Description">
         Lower quality levels produce grainier JPEG images with more noticeable 
         compression artifacts, but lower quality levels also use less network 
         bandwidth and CPU time.
    </dd>
    <dt class="Description-1 Description">JPEG chrominance subsampling</dt>
    <dd class="Description-1 Description">
         When compressing an image using JPEG, the RGB pixels are first 
         converted to the YCbCr colorspace, a colorspace in which each pixel is 
         represented as a brightness (Y, or &ldquo;luminance&rdquo;) value and a 
         pair of color (Cb &amp; Cr, or &ldquo;chrominance&rdquo;) values.  
         After this colorspace conversion, chrominance subsampling can be used 
         to discard some of the chrominance components in order to save 
         bandwidth.  This works because the human eye is more sensitive to 
         changes in brightness than to changes in color.  1X subsampling (the 
         default in TurboVNC) retains the chrominance components for all pixels, 
         and thus it provides the best image quality but also uses the most 
         network bandwidth and CPU time.  2X subsampling retains the chrominance 
         components for every other pixel, and 4X subsampling retains the 
         chrominance components for every fourth pixel (this is typically 
         implemented as 2X subsampling in both X and Y directions.)  Grayscale 
         throws out all of the chrominance components, leaving only luminance.  
         2X and 4X subsampling will typically produce noticeable blurring of 
         lines and other sharp features, but with photographic or other 
         &ldquo;smooth&rdquo; image content, it may be difficult to detect any 
         difference between 1X, 2X, and 4X.
    </dd>
    <dt class="Description-1 Description">Compression level</dt>
    <dd class="Description-1 Description">
         In TurboVNC, the compression level specifies: 
         <ol class="Ordered numeric"><li class="Ordered-0">
            the level of zlib compression that will be used with indexed color, 
            mono, and raw subrectangles
        </li>
        <li class="Ordered-0">
            the &ldquo;palette threshold&rdquo; (the minimum number of colors 
            that a 
            subrectangle must have before it is encoded as JPEG or raw instead 
            of 
            indexed color)
        </li>
        <li class="Ordered-0">
            whether or not <a href="#InterframeComparison">interframe 
            comparison</a><a name="idx0030"></a> should be used
        </li></ol> See Section 
        <a href="#AdvancedCompression" class="ref">7.2</a> below for more 
        details.
    </dd>
</dl>

<p>These parameters can be adjusted by accessing the TurboVNC Viewer 
Options dialog box (click on the &ldquo;Options&rdquo; button in the 
&ldquo;TurboVNC Connection&rdquo; dialog box or, after connecting to the 
server, click on the Connection Options button in the toolbar.)</p>

<p>The TurboVNC Viewer provides five preset &ldquo;encoding methods&rdquo;, 
corresponding to the most useful combinations of the image compression 
options described above:</p>

<a name="tab007001"></a>
<div class="table">
<table class="standard" summary="TurboVNC Encoding Methods">
<caption>Table 7.1: TurboVNC Encoding Methods</caption>
  <thead class="standard">
  <tr class="head ">
    <th class="head standard">Encoding method</th>
    <th class="head standard">Allow JPEG</th>
    <th class="head standard">JPEG image quality</th>
    <th class="head standard">JPEG chrominance subsampling</th>
    <th class="head standard">Compression level</th>
    <th class="head standard">Notes</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="standard">&ldquo;Tight + Perceptually Lossless JPEG&rdquo;</td>
    <td class="standard">Yes</td>
    <td class="standard">95</td>
    <td class="standard">1x</td>
    <td class="standard">1</td>
    <td class="standard">This encoding method should be perceptually lossless (that is, any image compression artifacts it produces should be imperceptible to human vision) under most viewing conditions.  This encoding method requires a great deal of network bandwidth, however, and is generally not recommended except on 50 Megabit/second and faster networks.</td>
  </tr>
  <tr class="standard">
    <td class="standard">&ldquo;Tight + Medium-Quality JPEG&rdquo;</td>
    <td class="standard">Yes</td>
    <td class="standard">80</td>
    <td class="standard">2x</td>
    <td class="standard">6</td>
    <td class="standard">For subrectangles that have a high number of unique colors, this encoding method produces some minor, but generally not very noticeable, image compression artifacts.  All else being equal, this encoding method typically uses about twice the network bandwidth of the &ldquo;Tight + Low-Quality JPEG&rdquo; encoding method and about half the bandwidth of the &ldquo;Tight + Perceptually Lossless JPEG&rdquo; encoding method, making it appropriate for medium-speed networks such as 10 Megabit Ethernet.  Interframe comparison is enabled with this encoding method (Compression Level 6 = Compression Level 1 + interframe comparison.)</td>
  </tr>
  <tr class="standard">
    <td class="standard">&ldquo;Tight + Low-Quality JPEG&rdquo;</td>
    <td class="standard">Yes</td>
    <td class="standard">30</td>
    <td class="standard">4x</td>
    <td class="standard">7</td>
    <td class="standard">For subrectangles that have a high number of unique colors, this encoding method produces very noticeable image compression artifacts.  However, it performs optimally on low-bandwidth connections.  If image quality is more critical than performance, then use one of the other encoding methods or take advantage of the <a href="#LR">Lossless Refresh feature</a><a name="idx0031"></a>.  In addition to reducing the JPEG quality to a &ldquo;minimum usable&rdquo; level, this encoding method also enables interframe comparison and Compression Level 2 (CL 7 = CL 2 + interframe comparison.)  Compression Level 2 can reduce bandwidth for low-color application workloads that are not good candidates for JPEG compression.</td>
  </tr>
  <tr class="standard">
    <td class="standard">&ldquo;Lossless Tight&rdquo;</td>
    <td class="standard">No</td>
    <td class="standard">N/A</td>
    <td class="standard">N/A</td>
    <td class="standard">0</td>
    <td class="standard">This encoding method uses indexed color subencoding for subrectangles that have a low number of unique colors, but it otherwise does not perform any image compression at all.  Lossless Tight is thus suitable only for gigabit and faster networks.  This encoding method uses significantly less CPU time than any of the JPEG-based encoding methods.  Lossless Tight requires an RFB protocol extension that is, as of this writing, only supported by the TurboVNC Viewer.</td>
  </tr>
  <tr class="standard">
    <td class="standard">&ldquo;Lossless Tight + Zlib&rdquo;</td>
    <td class="standard">No</td>
    <td class="standard">N/A</td>
    <td class="standard">N/A</td>
    <td class="standard">6</td>
    <td class="standard">This encoding method uses indexed color subencoding for subrectangles that have a low number of unique colors and raw subencoding for subrectangles that have a high number of unique colors.  It compresses all subrectangles using zlib with zlib compression level 1.  For certain types of low-color workloads (CAD applications, in particular), this encoding method may use less network bandwidth than the &ldquo;Tight + Perceptually Lossless JPEG&rdquo; encoding method, but it also uses significantly more CPU time than any of the JPEG-based encoding methods.  Interframe comparison is enabled with this encoding method (Compression Level 6 = Compression Level 1 + interframe comparison.)</td>
  </tr>
</table>
</div>


<p>The encoding method can be set in the TurboVNC Viewer Options dialog box 
(click on the &ldquo;Options&rdquo; button in the &ldquo;TurboVNC 
Connection&rdquo; dialog box or, after connecting to the server, click 
on the Connection Options button in the toolbar.)</p>


<h2 id="hd007001">7.1&nbsp;Interframe Comparison</h2>

<p><a name="InterframeComparison"></a></p>

<p>Certain ill-behaved applications can sometimes draw the same thing over 
and over again, and this can cause redundant framebuffer updates to be 
sent to the VNC viewer.  Additionally, modern GUI toolkits often use 
image-based drawing methods (the X Rendering Extension, for instance), 
which can result in an entire window being redrawn, even if only a few 
pixels in the window have changed.  The TurboVNC Server can guard 
against this by maintaining a copy of the remote framebuffer for each 
connected viewer, comparing each new framebuffer update rectangle 
against the pixels in the framebuffer copy, and discarding any redundant 
portions of the rectangle before they are sent to the viewer.</p>

<p>Interframe comparison has some tradeoffs associated with it.  Perhaps 
the most important of these is that it increases the memory usage of the 
TurboVNC Server by a factor of N, where N is the number of connected 
viewers.  This can prove to be quite significant if the remote desktop 
size is relatively large.</p>

<p>2D applications are most often the ones that generate duplicate 
framebuffer updates, so using interframe comparison with such 
applications can significantly reduce the network usage and the host CPU 
usage (since fewer rectangles are actually being encoded.)  However, 
with 3D applications, the benefits of interframe comparison are less 
clear, since it is less common for those applications to generate 
duplicate framebuffer updates.  Interframe comparison may benefit 
certain classes of 3D applications, such as design applications that 
render a model against a static background&ndash; particularly when the 
model is not zoomed in enough to fill the entire window.  In real-world 
tests, however, interframe comparison rarely reduces the network usage 
for 3D applications by more than 5-10%.  Furthermore, with games and 
other immersive applications that modify most of the pixels on the 
screen each time a frame is rendered, interframe comparison can actually 
increase both CPU usage and network usage.  Furthermore, the effects of 
duplicate framebuffer updates are not typically noticeable on high-speed 
networks, but an increase in host CPU usage might be.</p>

<p>For these reasons, interframe comparison is not enabled by default and 
should not generally be enabled except on bandwidth-constrained networks 
and with applications for which it can be shown to be beneficial.  
Interframe comparison can be enabled by either passing an argument of 
<code>-interframe</code> to <code>vncserver</code> when starting a 
TurboVNC session or by requesting a compression level of 5 or higher 
from the viewer (see below.)</p>



<h2 id="hd007002">7.2&nbsp;Advanced Compression Options</h2>

<p><a name="AdvancedCompression"></a></p>

<p>One of the underlying principles of TurboVNC&rsquo;s design is to expose 
only the options that have proven to be useful (that is, the options 
that have proven to have good performance tradeoffs.)  Thus, the 
TurboVNC Viewer GUI will normally only allow you to select Compression 
Levels 1-2 if JPEG subencoding is enabled (6-7 if interframe comparison 
is also enabled) or Compression Levels 0-1 if JPEG subencoding is 
disabled (5-6 if interframe comparison is enabled.)  Other compression 
levels can, however, be specified on the command line, and doing so will 
enable a compatibility mode in the TurboVNC Viewer GUI that allows any 
compression level from 0 to 9 to be requested.</p>

<p>When connecting to a TurboVNC server, requesting a particular 
compression level has the following effect:</p>

<a name="tab007002"></a>
<div class="table">
<table class="standard" summary="Compression Levels Supported by the TurboVNC Server (JPEG Enabled)">
<caption>Table 7.2: Compression Levels Supported by the TurboVNC Server (JPEG Enabled)</caption>
  <thead class="standard">
  <tr class="head ">
    <th class="head standard">Compression level</th>
    <th class="head standard">Zlib compression level (non-JPEG subrectangles)</th>
    <th class="head standard">Palette threshold</th>
    <th class="head standard">Interframe comparison</th>
    <th class="head standard">Notes</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="standard">0</td>
    <td class="standard">1</td>
    <td class="standard">24</td>
    <td class="standard">No</td>
    <td class="standard">Same as Compression Level 1.  Bypassing zlib when JPEG is enabled would only reduce the CPU usage for non-JPEG subrectangles, which is of limited usefulness.  Further, bypassing zlib requires an RFB protocol extension that is not supported by non-TurboVNC viewers.  It is presumed that, if one wants to reduce the CPU usage, then one wants to do so for all subrectangles, so CL 0 without JPEG (AKA &ldquo;Lossless Tight&rdquo;) should be used.</td>
  </tr>
  <tr class="standard">
    <td class="standard">1</td>
    <td class="standard">1</td>
    <td class="standard">24</td>
    <td class="standard">No</td>
    <td class="standard">See the description of the &ldquo;Tight + JPEG&rdquo; encoding methods above.</td>
  </tr>
  <tr class="standard">
    <td class="standard">2</td>
    <td class="standard">3</td>
    <td class="standard">96</td>
    <td class="standard">No</td>
    <td class="standard">A higher palette threshold causes indexed color subencoding to be used more often than with CL 1, and indexed color subrectangles are compressed using a higher zlib compression level.  This can provide typically 20-40% better compression than CL 1 (with a commensurate increase in CPU usage) for workloads that have a low number of unique colors.  However, Compression Level 2 can increase the CPU usage for some high-color workloads without providing significantly better compression.</td>
  </tr>
  <tr class="standard">
    <td class="standard">3-4</td>
    <td class="standard">3</td>
    <td class="standard">96</td>
    <td class="standard">No</td>
    <td class="standard">Same as Compression Level 2 (reserved for future expansion)</td>
  </tr>
  <tr class="standard">
    <td class="standard">5-6</td>
    <td class="standard">1</td>
    <td class="standard">24</td>
    <td class="standard">Yes</td>
    <td class="standard">Same as Compression Level 1, but with interframe comparison enabled</td>
  </tr>
  <tr class="standard">
    <td class="standard">7-8</td>
    <td class="standard">3</td>
    <td class="standard">96</td>
    <td class="standard">Yes</td>
    <td class="standard">Same as Compression Level 2, but with interframe comparison enabled</td>
  </tr>
  <tr class="standard">
    <td class="standard">9</td>
    <td class="standard">7</td>
    <td class="standard">256</td>
    <td class="standard">Yes</td>
    <td class="standard">This mode is included only for backward compatibility with TightVNC.  It provides approximately the same level of compression for 2D applications as Compression Level 9 in TightVNC 1.3.x, while using much less CPU time.  It also provides much better compression than TightVNC for 3D and video applications.  However, relative to Compression Level 2, this mode uses approximately twice as much CPU time and only achieves about 10-20% better average compression for 2D apps (and has no noticeable benefit for 3D and video apps.)  Thus, its usefulness is generally very limited.</td>
  </tr>
</table>
</div>


<p></p>

<a name="tab007003"></a>
<div class="table">
<table class="standard" summary="Compression Levels Supported by the TurboVNC Server (JPEG Disabled)">
<caption>Table 7.3: Compression Levels Supported by the TurboVNC Server (JPEG Disabled)</caption>
  <thead class="standard">
  <tr class="head ">
    <th class="head standard">Compression Level</th>
    <th class="head standard">Zlib compression level (indexed color subrectangles)</th>
    <th class="head standard">Zlib compression level (raw subrectangles)</th>
    <th class="head standard">Palette threshold</th>
    <th class="head standard">Interframe comparison</th>
    <th class="head standard">Notes</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="standard">0</td>
    <td class="standard">None</td>
    <td class="standard">None</td>
    <td class="standard">Subrectangle size / 4</td>
    <td class="standard">No</td>
    <td class="standard">See the description of the &ldquo;Lossless Tight&rdquo; encoding method above.</td>
  </tr>
  <tr class="standard">
    <td class="standard">1</td>
    <td class="standard">1</td>
    <td class="standard">1</td>
    <td class="standard">Subrectangle size / 96</td>
    <td class="standard">No</td>
    <td class="standard">See the description of the &ldquo;Lossless Tight + Zlib&rdquo; encoding method above.</td>
  </tr>
  <tr class="standard">
    <td class="standard">2-4</td>
    <td class="standard">1</td>
    <td class="standard">1</td>
    <td class="standard">Subrectangle size / 96</td>
    <td class="standard">No</td>
    <td class="standard">Same as Compression Level 1 (reserved for future expansion)</td>
  </tr>
  <tr class="standard">
    <td class="standard">5</td>
    <td class="standard">None</td>
    <td class="standard">None</td>
    <td class="standard">Subrectangle size / 4</td>
    <td class="standard">Yes</td>
    <td class="standard">Same as Compression Level 0, but with interframe comparison enabled</td>
  </tr>
  <tr class="standard">
    <td class="standard">6-8</td>
    <td class="standard">1</td>
    <td class="standard">1</td>
    <td class="standard">Subrectangle size / 96</td>
    <td class="standard">Yes</td>
    <td class="standard">Same as Compression Level 1, but with interframe comparison enabled</td>
  </tr>
  <tr class="standard">
    <td class="standard">9</td>
    <td class="standard">7</td>
    <td class="standard">5</td>
    <td class="standard">Subrectangle size / 96</td>
    <td class="standard">Yes</td>
    <td class="standard">This mode is included only for backward compatibility with TightVNC.  It provides approximately the same level of compression for 2D applications as Compression Level 9 in TightVNC 1.3.x, while using much less CPU time.  It also provides much better compression than TightVNC for 3D and video applications.  However, relative to Compression Level 1, this mode uses approximately twice as much CPU time and only achieves about 10% better average compression for 2D apps (and has no noticeable benefit for 3D and video apps.)  Thus, its usefulness is generally very limited.</td>
  </tr>
</table>
</div>




<h2 id="hd007003">7.3&nbsp;Lossless Refresh</h2>

<p><a name="LR"></a></p>

<p>Since both of TurboVNC&rsquo;s mathematically lossless encoding methods 
have performance drawbacks, another option for image-quality-critical 
applications is the &ldquo;Lossless Refresh&rdquo; feature.  When a 
lossless refresh is requested by a TurboVNC viewer, the server will send 
a mathematically lossless image of the current TurboVNC desktop to the 
requesting viewer.  So, for instance, a user can rotate/pan/zoom an 
object in their 3D application using a very low-quality JPEG setting, 
then when that user is ready to interpret or analyze the object, they 
can request a lossless refresh of TurboVNC&rsquo;s virtual screen.</p>

<p>To perform a lossless refresh, press CTRL-ALT-SHIFT-L or click on the 
Lossless Refresh toolbar icon.</p>



<h2 id="hd007004">7.4&nbsp;Automatic Lossless Refresh</h2>

<p><a name="ALR"></a></p>

<p>Passing an argument of <code>-alr <em>timeout</em></code> to 
<code>vncserver</code> will enable the automatic lossless refresh (ALR) 
feature for the TurboVNC session.  ALR will monitor all of the VNC 
viewer connections, and if more than <em><code>timeout</code></em> 
seconds have elapsed since the last framebuffer update was sent to a 
given viewer, then the TurboVNC Server will send to that viewer a 
mathematically lossless copy of any &ldquo;ALR-eligible&rdquo; screen 
regions that have been affected by lossy compression.  You can also pass 
arguments of <code>-alrqual</code> and <code>-alrsamp</code> to 
<code>vncserver</code> to specify that automatic lossless refreshes 
should be sent using JPEG instead (see the <code>Xvnc</code> man page 
for details.)</p>

<p>The ALR feature is designed mainly for use with interactive 
visualization applications.  The idea is that, on a low-bandwidth 
connection, low-quality JPEG can be used while the 3D scene is 
rotated/panned/zoomed, but when the motion stops, a fully lossless copy 
of the 3D image is sent and can be studied in detail.</p>

<p>The default is for any regions drawn with <code>X[Shm]PutImage()</code> 
to be ALR-eligible, as well as any regions drawn with CopyRect, if the 
source of the CopyRect operation was affected by lossy compression 
(CopyRect is an RFB encoding that allows the server to request that the 
viewer move a rectangle of pixels from one location to another.)  When 
used with VirtualGL, this means that ALRs will mainly be sent for just 
the 3D screen regions.  This should be fine for most 3D applications, 
since the 3D regions are the ones that are quality-critical.  The 
default ALR behavior also prevents what might best be called the 
&ldquo;blinking cursor dilemma.&rdquo;  Certain programs have a blinking 
cursor that may update more frequently than the ALR timeout.  Since an 
ALR is triggered based on a period of inactivity relative to the last 
framebuffer update, these continuous updates prevent an ALR from ever 
being sent. Fortunately, blinking cursors are not typically drawn using 
<code>X[Shm]PutImage()</code>, so the problem is effectively worked 
around by limiting the ALR-eligible regions to just the subset of 
regions that were drawn with <code>X[Shm]PutImage()</code> and CopyRect.</p>

<div class="important"><p class="important">
NOTE: Ill-behaved applications that continuously render the same image will cause a variation of the &ldquo;blinking cursor dilemma&rdquo; and thus defeat ALR unless <a href="#InterframeComparison">interframe comparison</a><a name="idx0032"></a> is enabled.
</p></div>

<p>You can override the default ALR behavior, thus making all screen 
regions eligible for ALR, by setting the <code>TVNC_ALRALL</code> 
environment variable to <code>1</code> on the TurboVNC host prior to 
starting a TurboVNC session.  You can also set 
<code>TVNC_ALRCOPYRECT</code> to <code>0</code> to make CopyRect regions 
ALR-ineligible, which approximates the behavior of TurboVNC 1.2.1 and 
prior.</p>



<h2 id="hd007005">7.5&nbsp;Multithreading</h2>

<p><a name="Multithreading"></a></p>

<p>By default, the TurboVNC Server uses multiple threads to perform image 
encoding and compression, thus allowing it to take advantage of 
multi-core or multi-processor systems.  The server splits the screen 
vertically into N tiles, where N is the number of threads, and assigns 
each tile to a separate thread. The scalability of this algorithm is 
nearly linear when used with demanding 3D or video applications that 
fill most of the screen.  However, whether or not multithreading 
improves the overall performance of TurboVNC depends largely on the 
performance of the viewer and the network.  If either the viewer or the 
network is the primary performance bottleneck, then enabling 
multithreading in the server will not help.  Multithreading is also not 
currently implemented with non-Tight encoding types.</p>

<p>To disable server-side multithreading, set the <code>TVNC_MT</code> 
environment variable to <code>0</code> on the host prior to starting 
<code>vncserver</code>, or pass an argument of <code>-nomt</code> to 
<code>vncserver</code>.  The default behavior is to use as many threads 
as there are cores on the TurboVNC host (up to a maximum of 4), but you 
can set the <code>TVNC_NTHREADS</code> environment variable or pass an 
argument of <code>-nthreads</code> to <code>vncserver</code> to override 
this.</p>

<p><br /></p>

<hr class="break" />



<h1 id="hd008"><a name="file008"></a>8&nbsp;TurboVNC Security Extensions</h1>

<p><a name="Security_Extensions"></a></p>


<h2 id="hd008001">8.1&nbsp;Terminology</h2>

<p>In an attempt to maintain consistency with other VNC implementations, 
TurboVNC uses the following terminology when referring to its security 
extensions:</p>

<dl class="Description">
    <dt class="Description-1 Description">Authentication Method</dt>
    <dd class="Description-1 Description">
         A technique that the VNC server uses to validate authentication 
         credentials sent from a VNC viewer.  If the credentials sent from a 
         particular VNC viewer are not valid, then that viewer is not allowed to 
         connect.
    </dd>
    <dt class="Description-1 Description">Authentication Scheme</dt>
    <dd class="Description-1 Description">
         A protocol used to send authentication credentials from a VNC viewer to 
         a VNC server for validation.  Some authentication schemes are required 
         by the RFB protocol specification, and others are implemented as 
         extensions to that specification.
    </dd>
    <dt class="Description-1 Description">Encryption Method</dt>
    <dd class="Description-1 Description">
         A technique used to encrypt the data sent between the VNC server and 
         the VNC viewer
    </dd>
    <dt class="Description-1 Description">Security Type</dt>
    <dd class="Description-1 Description">
         A specific combination of an authentication method, an authentication 
         scheme, and an encryption method
    </dd>
</dl>



<h2 id="hd008002">8.2&nbsp;TurboVNC Server Authentication Methods</h2>

<dl class="Description">
    <dt class="Description-1 Description">No Authentication</dt>
    <dd class="Description-1 Description">
         The VNC server does not authenticate the VNC viewer at all.
    </dd>
    <dt class="Description-1 Description">VNC Password Authentication</dt>
    <dd class="Description-1 Description">
         A session password sent from the VNC viewer is validated against a 
         password file, which is typically located under the user&rsquo;s home 
         directory on the VNC host.  The VNC password is separate from any other 
         login credentials and thus represents less of a security threat if 
         compromised (that is, assuming the VNC password and the user&rsquo;s 
         account password are not the same.)
    </dd>
    <dt class="Description-1 Description">One-Time Password (OTP) Authentication</dt>
    <dd class="Description-1 Description">
         Using the <code>vncpasswd</code> program, a unique password is 
         generated &ldquo;on the fly&rdquo; for the TurboVNC session, and the 
         password is printed on the command line (see the man page for 
         <code>vncpasswd</code> for more details.)  The user enters this 
         password in the VNC viewer, and the VNC viewer sends the password to 
         the server as if it were a VNC password.  However, once the OTP has 
         been used to authenticate a viewer, the OTP is forgotten and cannot be 
         reused.  OTP authentication can be used, for instance, to launch or 
         connect to TurboVNC sessions from an automated web portal or from a job 
         scheduler. OTP authentication is also useful for allowing temporary 
         access to a TurboVNC session for collaboration purposes.  The 
         <a href="#TurboVNC_Session_Manager">TurboVNC Session 
         Manager</a><a name="idx0033"></a> uses OTP authentication by default, 
         which allows it to securely authenticate with a TurboVNC session 
         without prompting for additional credentials.
    </dd>
    <dt class="Description-1 Description">PAM User/Password Authentication</dt>
    <dd class="Description-1 Description">
         The VNC server uses Pluggable Authentication Modules (PAM) to validate 
         a username and password received from a VNC viewer.  The password 
         received from the VNC viewer need not necessarily be validated against 
         the user&rsquo;s account password.  Generally, the TurboVNC Server can 
         validate the username and password using any authentication credentials 
         that can be accessed through PAM.  Since the user/password 
         authentication schemes supported by TurboVNC (see below) transmit the 
         password from the VNC viewer to the VNC server as plain text, it is 
         strongly recommended that the PAM User/Password authentication method 
         be used only with session encryption or if the session is restricted to 
         allow only loopback (SSH) connections and to disallow reverse 
         connections (see Section 
         <a href="#Secure_TurboVNC_Usage" class="ref">6.6</a>.)
    </dd>
</dl>



<h2 id="hd008003">8.3&nbsp;TurboVNC Viewer Authentication Schemes</h2>

<dl class="Description">
    <dt class="Description-1 Description">None</dt>
    <dd class="Description-1 Description">
         No authentication credentials are sent to the server.
    </dd>
    <dt class="Description-1 Description">Standard VNC Authentication</dt>
    <dd class="Description-1 Description">
         A password is sent to the server using a DES-encrypted 
         challenge/response scheme.  The password can be up to 8 characters 
         long, so the DES key length is 56 bits.  This is not a particularly 
         strong form of encryption by today&rsquo;s standards (56-bit DES was 
         broken by brute force attack in the late 90&rsquo;s.)
    </dd>
    <dt class="Description-1 Description">Unix Login/Plain Authentication</dt>
    <dd class="Description-1 Description">
         Both the username and password are sent to the VNC server as plain 
         text. Thus, it is <em>strongly</em> recommended that this 
         authentication scheme be used only with VNC connections that are 
         encrypted using TLS (see below) or SSH (see Section 
         <a href="#Secure_TurboVNC_Usage" class="ref">6.6</a>.)  Per the RFB 
         spec, this authentication scheme is referred to as &ldquo;Unix 
         Login&rdquo; when used with a TightVNC-compatible server and 
         &ldquo;Plain&rdquo; when used with a VeNCrypt-compatible server.
    </dd>
</dl>



<h2 id="hd008004">8.4&nbsp;Supported Encryption Methods</h2>

<p>TurboVNC supports three encryption methods:</p>

<dl class="Description">
    <dt class="Description-1 Description">None</dt>
    <dd class="Description-1 Description">
         No encryption
    </dd>
    <dt class="Description-1 Description">Anonymous TLS Encryption</dt>
    <dd class="Description-1 Description">
         The connection is encrypted using TLS (Transport Layer Security) 
         without authentication (i.e. without a certificate.)
    </dd>
    <dt class="Description-1 Description">TLS/X.509 Encryption</dt>
    <dd class="Description-1 Description">
         The connection is encrypted using TLS with a specified X.509 
         certificate.
    </dd>
</dl>



<h2 id="hd008005">8.5&nbsp;Supported Security Types</h2>

<p>TurboVNC supports the following security types:</p>

<div class="table">
<table class="standard">
  <thead class="standard">
  <tr class="head ">
    <th class="head standard">Server Security Type</th>
    <th class="head standard">Authentication Method</th>
    <th class="head standard">Encryption Method</th>
    <th class="head standard">Viewer Security Type</th>
    <th class="head standard">Authentication Scheme</th>
    <th class="head standard">Compatibility</th>
  </tr>
  </thead>
  <tr class="standard">
    <td class="high standard">None</td>
    <td class="standard">None</td>
    <td class="standard">None</td>
    <td class="high standard">None</td>
    <td class="standard">None</td>
    <td class="standard">RFB 3.3+</td>
  </tr>
  <tr class="standard">
    <td class="high standard">VNC</td>
    <td class="standard">VNC Password</td>
    <td class="standard">None</td>
    <td class="high standard">VNC</td>
    <td class="standard">Standard VNC</td>
    <td class="standard">RFB 3.3+</td>
  </tr>
  <tr class="standard">
    <td class="high standard">OTP</td>
    <td class="standard">One-Time Password</td>
    <td class="standard">None</td>
    <td class="high standard">VNC</td>
    <td class="standard">Standard VNC</td>
    <td class="standard">RFB 3.3+</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Plain</td>
    <td class="standard">PAM User/Password</td>
    <td class="standard">None</td>
    <td class="high standard">Plain</td>
    <td class="standard">Plain</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">TLSNone</td>
    <td class="standard">None</td>
    <td class="standard">Anonymous TLS</td>
    <td class="high standard">TLSNone</td>
    <td class="standard">None</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">TLSVnc</td>
    <td class="standard">VNC Password</td>
    <td class="standard">Anonymous TLS</td>
    <td class="high standard">TLSVnc</td>
    <td class="standard">Standard VNC</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">TLSOtp</td>
    <td class="standard">One-Time Password</td>
    <td class="standard">Anonymous TLS</td>
    <td class="high standard">TLSVnc</td>
    <td class="standard">Standard VNC</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">TLSPlain</td>
    <td class="standard">PAM User/Password</td>
    <td class="standard">Anonymous TLS</td>
    <td class="high standard">TLSPlain</td>
    <td class="standard">Plain</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">X509None</td>
    <td class="standard">None</td>
    <td class="standard">TLS/X.509</td>
    <td class="high standard">X509None</td>
    <td class="standard">None</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">X509Vnc</td>
    <td class="standard">VNC Password</td>
    <td class="standard">TLS/X.509</td>
    <td class="high standard">X509Vnc</td>
    <td class="standard">Standard VNC</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">X509Otp</td>
    <td class="standard">One-Time Password</td>
    <td class="standard">TLS/X.509</td>
    <td class="high standard">X509Vnc</td>
    <td class="standard">Standard VNC</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">X509Plain</td>
    <td class="standard">PAM User/Password</td>
    <td class="standard">TLS/X.509</td>
    <td class="high standard">X509Plain</td>
    <td class="standard">Plain</td>
    <td class="standard">RFB 3.7+ with VeNCrypt extensions</td>
  </tr>
  <tr class="standard">
    <td class="high standard">UnixLogin</td>
    <td class="standard">PAM User/Password</td>
    <td class="standard">None</td>
    <td class="high standard">UnixLogin</td>
    <td class="standard">Unix Login</td>
    <td class="standard">RFB 3.7+ with TightVNC extensions</td>
  </tr>
</table>
</div>


<div class="important"><p class="important">
NOTE: The security type names are case-insensitive.  The capitalization conventions above are used in order to maintain consistency with the RFB protocol specification.
</p></div>



<h2 id="hd008006">8.6&nbsp;Enabling Security Types</h2>

<p>The default behavior of the TurboVNC Server is for all security types 
except &ldquo;TLSNone&rdquo;, &ldquo;X509None&rdquo;, and 
&ldquo;None&rdquo; to be enabled and for VNC Password and OTP 
authentication to be preferred over PAM User/Password authentication.  
However, the system administrator can disable one or more of the 
security types or set the preferred order of the security types by 
editing the TurboVNC security configuration file.  See the 
<code>Xvnc</code> man page for more details.</p>

<p>If the VNC server allows multiple security types, then the VNC 
viewer&rsquo;s default security type will be determined by the 
server&rsquo;s preferred security type.  In this case, the user can 
override the default by passing command-line arguments to 
<code>vncviewer</code>.  If the VNC server prefers a security type that 
supports Standard VNC authentication, then the user can force the use of 
Unix Login/Plain authentication by passing an argument of <code>-user 
<em>user-name</em></code> to <code>vncviewer</code> when connecting to 
the TurboVNC session.  Similarly, if the VNC server prefers a security 
type that supports Unix Login/Plain authentication, then the user can 
force the use of Standard VNC authentication by passing an argument of 
<code>-nounixlogin</code> to <code>vncviewer</code>. You can also 
accomplish the same thing by unchecking &ldquo;Unix Login&rdquo; or 
&ldquo;Plain&rdquo; or &ldquo;Standard VNC&rdquo; in the 
&ldquo;Security&rdquo; tab of the Options dialog or by limiting the 
available security types using the <code>SecurityTypes</code>, 
<code>User</code>, or <code>NoUnixLogin</code> arguments/parameters.</p>

<p>If the system administrator has not restricted any of the server 
security types on a system-wide basis, then the user can choose to 
disable some or all of them for a particular TurboVNC session by using 
the <code>-SecurityTypes</code> command-line argument when starting the 
session.  See the <code>Xvnc</code> man page for more details.</p>



<h2 id="hd008007">8.7&nbsp;Further Reading</h2>

<p>For more detailed information about the TurboVNC security extensions, 
refer to the TurboVNC man pages:</p>

<pre class="verbatim">
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;vncserver
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;Xvnc
man&nbsp;-M&nbsp;/opt/TurboVNC/man&nbsp;vncpasswd
</pre>

<p><br /></p>

<hr class="break" />



<h1 id="hd009"><a name="file009"></a>9&nbsp;Hardware 3D Acceleration (Using VirtualGL with TurboVNC)</h1>

<p><a name="VGL"></a></p>

<p>Referring to the VirtualGL User&rsquo;s Guide, VirtualGL&rsquo;s X11 
Transport draws OpenGL-rendered frames onto an X display using standard 
X11 drawing commands. Since this results in the frames being sent 
uncompressed to the X server, the X11 Transport is designed to be used 
with an &ldquo;X proxy.&rdquo;  An X proxy acts as a virtual X server, 
receiving X11 commands from applications (and from VirtualGL), rendering 
the X11 commands into images, compressing the resulting images, and 
sending the compressed images over the network to a client or clients.</p>

<p>Since VirtualGL is sending rendered frames to the X proxy at a very fast 
rate, the proxy must be able to compress the frames very quickly in 
order to keep up. Unfortunately, however, most X proxies can&rsquo;t.  
They simply aren&rsquo;t designed to compress, with any degree of 
performance, the large and complex images generated by 3D applications.</p>

<p>Enter TurboVNC.  Although TurboVNC can be used with all types of 
applications, it was initially designed as a fast X proxy for VirtualGL.  
TurboVNC provides an alternate means of delivering rendered frames from 
VirtualGL to a client machine without using VirtualGL&rsquo;s built-in 
VGL Transport.</p>


<h3 id="hd009000001">Advantages of TurboVNC (when compared to the VGL Transport)</h3>

<ul class="Itemize">
    <li class="Itemize-1 Itemize asterisk">
        When using the VGL Transport, non-OpenGL elements of the 3D 
        application&rsquo;s GUI are sent over the network using remote X11, 
        which will create performance problems on high-latency networks (such as 
        broadband or long-haul fibre.)  Non-OpenGL elements of the 3D 
        application&rsquo;s GUI will load and render much faster (perhaps even 
        orders of magnitude faster) with TurboVNC than with the VGL Transport on 
        such connections.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        For 3D applications whose rendered frames do not contain very many 
        unique colors (for instance, CAD applications in wireframe mode), the 
        hybrid encoding methods used by TurboVNC will generally use less network 
        bandwidth than the pure JPEG encoding method used by the VGL Transport.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC provides two lossless compression modes, one of which is 
        designed to reduce host CPU usage on gigabit networks and the other of 
        which is designed to provide reasonable performance on wide-area 
        networks (at the expense of higher host CPU usage.)  The VGL 
        Transport&rsquo;s only lossless option is uncompressed RGB.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC includes a lossless refresh feature that will, on demand, send 
        a mathematically lossless image of the remote desktop to the client.  A 
        user connecting over a low-bandwidth connection can use low-quality JPEG 
        to achieve the best performance when manipulating a 3D model, then they 
        can request a lossless refresh when they are ready to study the model in 
        detail.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        The TurboVNC Server can be configured to send, during periods of 
        inactivity, a mathematically lossless copy of the rendered frames drawn 
        by VirtualGL (Automatic Lossless Refresh.)
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC provides rudimentary collaboration capabilities.  Multiple 
        users can simultaneously view the same TurboVNC session and pass around 
        control of the keyboard and mouse.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        From the point of view of the 3D application, the TurboVNC client/server 
        connection is stateless.  If the network hiccups or the viewer is 
        otherwise disconnected, the TurboVNC session continues to run on the 
        host and can be rejoined from any machine on the network.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        No X server is required on the client machine.  This reduces the 
        deployment complexity for Windows clients.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Any machine with a web browser, and any mobile device, can be used as a 
        TurboVNC client (with reduced performance and features relative to the 
        TurboVNC Viewer.)
    </li>
</ul>



<h3 id="hd009000002">Disadvantages of TurboVNC (when compared to the VGL transport)</h3>

<ul class="Itemize">
    <li class="Itemize-1 Itemize asterisk">
        No seamless windows.  All application windows are constrained to a 
        &ldquo;virtual desktop&rdquo;, which displays in a single window on the 
        client machine.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC will generally require about 20% more host/server CPU cycles to 
        maintain the same frame rate as the VGL Transport, both because it has 
        to compress more pixels in each frame (an entire desktop rather than a 
        single window) and because it has to perform 2D (X11) rendering as well 
        as 3D rendering.
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC does not support quad-buffered stereo or transparent overlays.
    </li>
</ul>



<h2 id="hd009001">9.1&nbsp;Using VirtualGL on a TurboVNC Host</h2>

<p>The most common (and optimal) way to use VirtualGL with TurboVNC is to 
configure the same machine as a TurboVNC host and a VirtualGL server.  
This allows VirtualGL to send rendered frames to TurboVNC through shared 
memory rather than over a network.</p>

<div class="figure">
<img src="x11transport.png" alt="x11transport" class="figure" id="imgid_8" name="imgid_8"/>
</div>

<p>The following procedure describes how to launch a 3D application using 
this configuration.</p>


<h3 id="hd009001001">Procedure</h3>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered">
        Follow the procedure described in Chapter 
        <a href="#TurboVNC_Usage" class="ref">6</a> for starting a TurboVNC 
        session and connecting to it.
    </li>
    <li class="Ordered-1 Ordered">
        Open a new terminal inside the TurboVNC desktop.
    </li>
    <li class="Ordered-1 Ordered">
        In the terminal, start a 3D application using VirtualGL:
        <pre class="verbatim">/opt/VirtualGL/bin/vglrun <em>[vglrun options]</em> <em>3D-application-executable-or-script</em> <em>[arguments]</em></pre>
    </li>
</ol>



<h2 id="hd009002">9.2&nbsp;Using VirtualGL on a Machine Other Than a TurboVNC Host</h2>

<div class="figure">
<img src="vgltransportservernetwork.png" alt="vgltransportservernetwork" class="figure" id="imgid_9" name="imgid_9"/>
</div>

<p>If the TurboVNC host and VirtualGL server are different machines, then 
it is desirable to use the VGL Transport to send rendered frames from 
the VirtualGL server to the TurboVNC session.  It is also desirable to 
disable image compression in the VGL Transport.  Otherwise, the images 
would have to be compressed by the VirtualGL server, decompressed by the 
VirtualGL Client, then recompressed by the TurboVNC Server, which is a 
waste of CPU resources. However, sending images uncompressed over a 
network requires a fast network (generally, Gigabit Ethernet or faster), 
so there needs to be a fast link between the VirtualGL server and the 
TurboVNC host for this procedure to perform well.</p>


<h3 id="hd009002001">Procedure</h3>

<ol class="Ordered numeric">
    <li class="Ordered-1 Ordered">
        Follow the procedure described in Chapter 
        <a href="#TurboVNC_Usage" class="ref">6</a> for starting a TurboVNC 
        session and connecting to it.
    </li>
    <li class="Ordered-1 Ordered">
        Open a new terminal inside the TurboVNC desktop.
    </li>
    <li class="Ordered-1 Ordered">
        In the same terminal window, open a Secure Shell (SSH) session into the 
        VirtualGL server:
        <pre class="verbatim">/opt/VirtualGL/bin/vglconnect <em>user</em>@<em>server</em></pre>
        Replace <em><code>user</code></em> with your username on the VirtualGL 
        server and <em><code>server</code></em> with the hostname or IP address 
        of that server.  Refer to the VirtualGL User&rsquo;s Guide for 
        additional <code>vglconnect</code> options.
    </li>
    <li class="Ordered-1 Ordered">
        In the SSH session, set the <code>VGL_COMPRESS</code> environment 
        variable to <code>rgb</code>
        <div class="important"><p class="important">
        Passing an argument of <code>-c&nbsp;rgb</code> to <code>vglrun</code> achieves the same result.
        </p></div>
    </li>
    <li class="Ordered-1 Ordered">
        In the SSH session, start a 3D application using VirtualGL:
        <pre class="verbatim">/opt/VirtualGL/bin/vglrun <em>[vglrun options]</em> <em>3D-application-executable-or-script</em> <em>[arguments]</em></pre>
    </li>
</ol>



<h2 id="hd009003">9.3&nbsp;NV-CONTROL Emulation</h2>

<p>This version of TurboVNC includes partial emulation of the 
<code>NV-CONTROL</code> X11 extension provided by nVidia&rsquo;s 
proprietary Un*x drivers.  Certain 3D applications rely on this 
extension to query and set low-level GPU properties, and unfortunately 
the library (libXNVCtrl) used by applications to interact with the 
extension is static, making it impossible to interpose using VirtualGL.</p>

<p>Passing an argument of <code>-nvcontrol <em>display</em></code> to 
<code>vncserver</code> will set up a fake <code>NV-CONTROL</code> 
extension in the TurboVNC session and will redirect all 
<code>NV-CONTROL</code> requests to <em><code>display</code></em>.  
<em><code>display</code></em> should generally be the name of the 3D X 
server you plan to use with VirtualGL (<code>:0</code>, for instance.)  
The TurboVNC Server does not attempt to open a connection to this 
display until an application uses the <code>NV-CONTROL</code> extension.  
If a connection to the 3D X server cannot be opened, if the 3D X server 
does not have the <code>NV-CONTROL</code> extension, or if other issues 
are encountered when attempting to redirect <code>NV-CONTROL</code> 
requests, then a BadRequest X11 error will be returned to the 
application, and the TurboVNC session log will display an error message 
explaining why the request failed. It is assumed that you have already 
followed the procedure in the VirtualGL User&rsquo;s Guide to allow 
access to the 3D X server.  If access to the 3D X server is restricted 
to members of the <code>vglusers</code> group, then you may need to 
execute</p>

<pre class="verbatim">
xauth&nbsp;merge&nbsp;/etc/opt/VirtualGL/vgl_xauth_key
</pre>

<p>if you need to use the <code>NV-CONTROL</code> extension prior to 
invoking <code>vglrun</code> for the first time.</p>

<p>You can change the 3D X server for a particular TurboVNC session after 
the session has been started.  For instance, if you want to redirect 
both <code>NV-CONTROL</code> requests and OpenGL to a GPU attached to 
Screen 1 of Display :0, you would execute</p>

<pre class="verbatim">xprop -root -f VNC_NVCDISPLAY 8s -set VNC_NVCDISPLAY :0.1
vglrun -d :0.1 <em>3D-application-executable-or-script</em></pre>
<p><br /></p>

<hr class="break" />



<h1 id="hd0010"><a name="file010"></a>10&nbsp;Compatibility Guide</h1>

<p><a name="Compatibility"></a></p>

<p>In order to realize the full benefits of TurboVNC, it is necessary to 
use the TurboVNC Server and the TurboVNC Viewer in concert.  However, 
TurboVNC is fully compatible with TigerVNC, TightVNC, RealVNC, and other 
VNC flavors.  You can use the TurboVNC Viewer to connect to a 
non-TurboVNC server (or vice versa), although this will generally result 
in some decrease in performance, and features such as the 
<a href="#TurboVNC_Session_Manager">TurboVNC Session 
Manager</a><a name="idx0034"></a> will not be available.</p>

<p>The following sections list additional things to bear in mind when 
mixing TurboVNC with other VNC flavors.</p>


<h2 id="hd0010001">10.1&nbsp;TightVNC or TigerVNC Servers</h2>

<ul class="Itemize">
    <li class="Itemize-1 Itemize asterisk">
        TightVNC and TigerVNC specify the JPEG quality level on a scale from 0 
        to 9. This translates to actual JPEG quality as follows:
        <dl class="Description">
            <dt class="Description-3 Description">TightVNC JPEG Quality Levels</dt>
            <dd class="Description-3 Description">
                <div class="table">
                <table class="standard">
                  <thead class="standard">
                  <tr class="head ">
                    <th class="head standard">JPEG quality level</th>
                    <th class="head standard">0</th>
                    <th class="head standard">1</th>
                    <th class="head standard">2</th>
                    <th class="head standard">3</th>
                    <th class="head standard">4</th>
                    <th class="head standard">5</th>
                    <th class="head standard">6</th>
                    <th class="head standard">7</th>
                    <th class="head standard">8</th>
                    <th class="head standard">9</th>
                  </tr>
                  </thead>
                  <tr class="standard">
                    <td class="high standard">Actual JPEG quality</td>
                    <td class="standard">5</td>
                    <td class="standard">10</td>
                    <td class="standard">15</td>
                    <td class="standard">25</td>
                    <td class="standard">37</td>
                    <td class="standard">50</td>
                    <td class="standard">60</td>
                    <td class="standard">70</td>
                    <td class="standard">75</td>
                    <td class="standard">80</td>
                  </tr>
                  <tr class="standard">
                    <td class="high standard">Actual chrominance subsampling</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                  </tr>
                </table>
                </div>
                
        <a name="TigerVNC_JPEG_Qual"></a>
            </dd>
            <dt class="Description-3 Description">TigerVNC JPEG Quality Levels</dt>
            <dd class="Description-3 Description">
                <div class="table">
                <table class="standard">
                  <thead class="standard">
                  <tr class="head ">
                    <th class="head standard">JPEG quality level</th>
                    <th class="head standard">0</th>
                    <th class="head standard">1</th>
                    <th class="head standard">2</th>
                    <th class="head standard">3</th>
                    <th class="head standard">4</th>
                    <th class="head standard">5</th>
                    <th class="head standard">6</th>
                    <th class="head standard">7</th>
                    <th class="head standard">8</th>
                    <th class="head standard">9</th>
                  </tr>
                  </thead>
                  <tr class="standard">
                    <td class="high standard">Actual JPEG quality</td>
                    <td class="standard">15</td>
                    <td class="standard">29</td>
                    <td class="standard">41</td>
                    <td class="standard">42</td>
                    <td class="standard">62</td>
                    <td class="standard">77</td>
                    <td class="standard">79</td>
                    <td class="standard">86</td>
                    <td class="standard">92</td>
                    <td class="standard">100</td>
                  </tr>
                  <tr class="standard">
                    <td class="high standard">Actual chrominance subsampling</td>
                    <td class="standard">4X</td>
                    <td class="standard">4X</td>
                    <td class="standard">4X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">2X</td>
                    <td class="standard">1X</td>
                    <td class="standard">1X</td>
                    <td class="standard">1X</td>
                    <td class="standard">1X</td>
                  </tr>
                  <tr class="standard">
                    <td class="high standard">Average compression ratio *</td>
                    <td class="standard">100</td>
                    <td class="standard">80</td>
                    <td class="standard">70</td>
                    <td class="standard">60</td>
                    <td class="standard">50</td>
                    <td class="standard">40</td>
                    <td class="standard">30</td>
                    <td class="standard">25</td>
                    <td class="standard">20</td>
                    <td class="standard">10</td>
                  </tr>
                </table>
                </div>
                
                <div class="important"><p class="important">
                * Experimentally determined by compressing every 10th frame in the SPECviewperf 9 benchmark suite
                </p></div>
            </dd>
        </dl>
        TurboVNC, on the other hand, includes extensions to Tight encoding that 
        allow the JPEG quality to be specified on the standard 1-100 scale and 
        allow the JPEG chrominance subsampling to be specified seperately. 
        TigerVNC 1.2 (and later) includes the same extensions on the server 
        side, so the TigerVNC 1.2+ Server will behave like the TurboVNC Server 
        when a TurboVNC viewer is connected to it. <br /><br /> When a TurboVNC 
        viewer is connected to a TightVNC or TigerVNC 1.0/1.1 server, setting 
        the JPEG quality to N in the TurboVNC Viewer sets the JPEG quality level 
        to N/10 on the TightVNC or TigerVNC server.  For instance, if you set 
        the JPEG quality to 95 in the TurboVNC Viewer, this would translate to a 
        JPEG quality level of 9, which would set the actual JPEG 
        quality/subsampling to 80/2X if connected to a TightVNC server or 100/1X 
        if connected to a TigerVNC 1.0/1.1 server. <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Changing the JPEG chrominance subsampling option in the TurboVNC Viewer 
        has no effect when connected to a TightVNC or TigerVNC 1.0/1.1 server. 
        <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Normally, the TurboVNC Viewer GUI only allows you to select the 
        compression levels that are useful for TurboVNC servers, but you can 
        specify additional compression levels on the TurboVNC Viewer command 
        line.  You can also pass an argument of <code>-compatiblegui</code> to 
        the viewer to expose all 10 compression levels in the GUI, which is 
        useful when connecting to non-TurboVNC servers.  It should be noted, 
        however, that our experiments have shown that compression levels higher 
        than 5 are generally not useful in the TightVNC or TigerVNC Servers.  
        They increase CPU usage exponentially without providing any significant 
        savings in bandwidth relative to Compression Level 5. <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        TurboVNC supports an extension to Tight encoding that allows the server 
        to tell the viewer not to use zlib to decompress a particular 
        subrectangle.  Zlib introduces a tremendous amount of performance 
        overhead, even when zlib compression level 0 (no compression) is used.  
        Thus, when a TurboVNC viewer requests Compression Level 0 from the 
        TurboVNC Server, the TurboVNC Server bypasses zlib altogether.  TightVNC 
        and TigerVNC servers do not support this extension, and thus they will 
        still use zlib to &ldquo;compress&rdquo; the framebuffer updates even if 
        you request Compression Level 0 using the TurboVNC Viewer. <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        When properly configured, version 1.2 and later (except for versions 
        1.4.0 - 1.4.2, which contained a performance regression) of the TigerVNC 
        Server can be made to perform similarly to a single-threaded instance of 
        the TurboVNC Server.  However, all other versions of TigerVNC and 
        TightVNC will use much more CPU time across the board than the TurboVNC 
        Server, all else being equal.  With JPEG enabled, Compression Levels 1 
        and 2 in TigerVNC are roughly equivalent to the same compression levels 
        in TurboVNC, except that TigerVNC enables interframe comparison 
        automatically with Compression Level 2 and above.
    </li>
</ul>



<h2 id="hd0010002">10.2&nbsp;TightVNC or TigerVNC Viewers</h2>

<ul class="Itemize">
    <li class="Itemize-1 Itemize asterisk">
        The TurboVNC Server will attempt to emulate the behavior of a TigerVNC 
        server and will translate JPEG quality levels into actual JPEG quality 
        and subsampling, as specified in Section 
        <a href="#TigerVNC_JPEG_Qual" class="ref">10.1</a>. <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        When either a TightVNC or TigerVNC viewer is connected to a TurboVNC 
        server and JPEG subencoding is disabled, setting the compression level 
        to 0 in the viewer will cause the connection to abort with a &ldquo;bad 
        subencoding value&rdquo; error.  This is because the TurboVNC Server is 
        attempting to send the framebuffer updates with no zlib compression, and 
        the TightVNC and TigerVNC viewers don&rsquo;t support this. <br /><br /> 
        A similar issue occurs when using more than four encoding threads in the 
        server.  Since the Tight encoding type is limited to four zlib streams, 
        any encoding threads beyond the first four cannot use zlib compression. 
        <br /><br />
    </li>
    <li class="Itemize-1 Itemize asterisk">
        Refer to Section <a href="#AdvancedCompression" class="ref">7.2</a> for 
        a description of how the TurboVNC Server responds to requests for 
        Compression Levels 0-9. <br /><br />
    </li>
</ul>



<h2 id="hd0010003">10.3&nbsp;RealVNC</h2>

<p>The TurboVNC Viewer supports the Hextile, Raw, and ZRLE encoding types, 
which are compatible with RealVNC.  None of these encoding types can be 
selected from the TurboVNC Viewer GUI, but Hextile or ZRLE will be 
selected automatically when connecting to a RealVNC server.  Non-Tight 
encoding types, such as Hextile and Raw, can also be manually selected 
from the TurboVNC Viewer command line. In addition to Hextile, Raw, and 
ZRLE, the TurboVNC Server also supports the RRE, CoRRE, and Zlib legacy 
encoding types, for compatibility with older VNC viewers.</p>

<p>All of the non-Tight encoding types have performance drawbacks.  Raw 
encoding requires gigabit in order to achieve decent performance, and it 
can easily take up an entire gigabit connection&rsquo;s worth of 
bandwidth (it also doesn&rsquo;t perform particularly well with the 
TurboVNC Viewer, because of the need to convert the pixels from bytes to 
ints in Java.)  Hextile uses very small tiles, which causes it to incur 
a large amount of computational overhead.  It compresses too poorly to 
perform well on slow links but uses too much CPU time to perform well on 
fast links.  ZRLE improves upon this, but it is still too 
computationally intense for fast networks.  The <code>vncviewer</code> 
man page in the TurboVNC Linux packages has some additional information 
about how Hextile and ZRLE work.</p>

<p><br /></p>

<hr class="break" />



<h1 id="hd0011"><a name="file011"></a>11&nbsp;Advanced Configuration</h1>


<h2 id="hd0011001">11.1&nbsp;Server Settings</h2>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_ALRALL = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/Enable automatic lossless refresh for regions that were drawn using X11 functions other than <code>X[Shm]PutImage()</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        See Section <a href="#ALR" class="ref">7.4</a>
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_ALRCOPYRECT = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/Enable automatic lossless refresh for regions that were drawn using CopyRect</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Enabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        See Section <a href="#ALR" class="ref">7.4</a>
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_COMBINERECT = <em>{c}</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Combine framebuffer updates with more than <em><code>{c}</code></em> rectangles into a single rectangle spanning the bounding box of all of the constituent rectangles</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard"><code>100</code></td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        Applications can sometimes draw many thousands of points or tiny lines 
        using individual X11 calls, and this can cause the VNC server to send 
        many thousands of tiny rectangles to the VNC viewer.  The overhead 
        associated with this can bog down the viewer, and in extreme cases, the 
        number of rectangles may even exceed the maximum number that is allowed 
        in a single framebuffer update (65534.)  Thus, if a framebuffer update 
        contains more than <em><code>{c}</code></em> rectangles, TurboVNC will 
        coalesce it into a single rectangle that covers all of the rectangles in 
        the update.  For applications that generate many tiny rectangles, 
        increasing <code>TVNC_COMBINERECT</code> may significantly increase the 
        number of pixels sent to the viewer, which will increase network usage.  
        However, for those same applications, lowering 
        <code>TVNC_COMBINERECT</code> will increase the number of rectangles 
        sent to the viewer, which will increase the CPU usage of both the server 
        and the viewer.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_ICEBLOCKSIZE = <em>{s}</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Set the block size for the interframe comparison engine (ICE) to <em><code>{s}</code></em> x <em><code>{s}</code></em> pixels.  Setting <em><code>{s}</code></em> to 0 causes the ICE to compare full rectangles, as TurboVNC 1.2.x did.</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard"><code>256</code></td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        If interframe comparison is enabled (see Section 
        <a href="#InterframeComparison" class="ref">7.1</a>), then TurboVNC will 
        compare each rectangle of each framebuffer update on a block-by-block 
        basis and send only the blocks that have changed.  This prevents large 
        rectangles from being re-transmitted if only a few pixels in the 
        rectangle have changed.  Using smaller block sizes can decrease network 
        usage if only a few pixels are changing between updates, but using 
        smaller block sizes can also interfere with the Tight encoder&rsquo;s 
        ability to efficiently split rectangles into subrectangles, thus 
        increasing host CPU usage (and sometimes increasing network usage as 
        well, which runs counter to the purpose of interframe comparison.)  
        Setting the block size to 0 causes the ICE to compare full framebuffer 
        update rectangles, as TurboVNC 1.2.x did. <br /><br /> The default block 
        size of 256x256 was chosen based on extensive low-level experiments 
        using the same set of RFB session captures that were used when designing 
        the TurboVNC encoder.  For most of those datasets, 256x256 blocks 
        produced the lowest network and CPU usage, but actual mileage may vary. 
        There were rare cases in which using 64x64 blocks or full-rectangle 
        comparison produced better network and CPU usage.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_ICEDEBUG = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/Enable the ICE debugger</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        If interframe comparison is enabled (see Section 
        <a href="#InterframeComparison" class="ref">7.1</a>), then setting this 
        environment variable to 1 will cause the interframe comparison engine 
        (ICE) to change the color of duplicate screen regions without culling 
        them from the update stream. This allows you to easily see which 
        applications are generating duplicate updates.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_MT = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/Enable multithreaded image encoding</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Enabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        See Section <a href="#Multithreading" class="ref">7.5</a>
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_NTHREADS = <em>{n}</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Use <em><code>{n}</code></em> threads (1 &lt;= <em><code>{n}</code></em> &lt;= 8) to perform image encoding</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard"><em><code>{n}</code></em> = the number of CPU cores in the system, up to a maximum of 4</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        See Section <a href="#Multithreading" class="ref">7.5</a>
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_PROFILE = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable profiling output</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        If profiling output is enabled, then the TurboVNC Server will 
        continuously benchmark itself and periodically print the throughput of 
        various stages in its image pipeline to the Xvnc log file.
    </dd>
</dl>



<h2 id="hd0011002">11.2&nbsp;Viewer Settings</h2>

<p>Java system properties are normally specified as command-line arguments 
to the Java executable.  For example:</p>

<pre class="verbatim">java -Dmy.system.property=<em>value</em> -jar MyClass.jar</pre>
<p>However, since TurboVNC hides the Java command line inside of its 
startup scripts (or inside of an application bundle on macOS), the 
easiest way to set these properties is by using the 
<code>JAVA_TOOL_OPTIONS</code> environment variable, which allows you to 
specify Java command-line arguments even if you don&rsquo;t have access 
to the command line.  For instance, on Linux you could execute:</p>

<pre class="verbatim">
JAVA_TOOL_OPTIONS=-Dturbovnc.profile=1&nbsp;/opt/TurboVNC/bin/vncviewer
</pre>

<p>to start the TurboVNC Viewer without JPEG acceleration.</p>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.forcealpha = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable back buffer alpha channel</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Enabled if using OpenGL Java 2D blitting, disabled otherwise</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        If this property is enabled, then the TurboVNC Viewer will use a 
        TYPE_INT_ARGB_PRE (BGRA with pre-computed alpha channel) BufferedImage 
        as its back buffer instead of a TYPE_INT_RGB (BGRX) BufferedImage.  When 
        using OpenGL blitting in Java 2D (normally accomplished by passing an 
        argument of <code>-Dsun.java2d.opengl=true</code> to <code>java</code>), 
        it is generally faster to draw an alpha-enabled BufferedImage to the 
        screen, because otherwise glDrawPixels() has to set all of the alpha 
        values itself (which can cause it to revert to an unaccelerated code 
        path in some cases.)
        <div class="important"><p class="important">
        NOTE: this property is enabled by default when using Java 7 or later on Mac platforms, because OpenGL Java 2D blitting is the only option available.
        </p></div>
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.lionfs = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable the use of the macOS full-screen application feature</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Enabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        When running in full-screen mode, the TurboVNC Viewer will normally try 
        to take advantage of the full-screen application feature provided by OS 
        X/macOS 10.7 and later, if available.  Disabling this property will 
        force the viewer to use its own built-in cross-platform 
        &ldquo;pseudo-full-screen&rdquo; feature instead.  This is useful mainly 
        for testing.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.primary = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable the use of the X11 PRIMARY clipboard selection</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Enabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        X11 has two ways of copying/pasting text.  When text is selected in most 
        X11 applications, it is copied to the PRIMARY selection, and it can be 
        pasted by pressing the middle mouse button.  When text is explicitly 
        copied using a &ldquo;Copy&rdquo; menu option or a hotkey (such as 
        CTRL-C), it is copied to the CLIPBOARD selection, and it can only be 
        pasted by explicitly selecting a &ldquo;Paste&rdquo; menu option or 
        pressing a hotkey (such as CTRL-V.) Normally, on X11 platforms, the 
        TurboVNC Viewer transfers the PRIMARY selection from client to server 
        and, when receiving a clipboard update from the server, it sets both the 
        PRIMARY and CLIPBOARD selections with the server&rsquo;s clipboard 
        contents.  Disabling this property will cause only the the CLIPBOARD 
        selection to be transferred from client to server (in other words, the 
        clipboard will not be transferred unless you explicitly copy something 
        by using a menu option or hotkey), and clipboard changes from the server 
        will only affect the client&rsquo;s CLIPBOARD selection (in other words, 
        you will have to explicitly paste the server&rsquo;s clipboard contents 
        by using a menu option or hotkey on the client.)
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_PROFILE = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable profiling output</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        If profiling output is enabled, then the TurboVNC Viewer will 
        continuously benchmark itself and periodically print the throughput of 
        various stages in its image pipeline to the console.
    </dd>
</dl>

<p><a name="TVNC_SERVERARGS"></a></p>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_SERVERARGS</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.serverargs</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Additional arguments that the TurboVNC Session Manager will pass to <code>vncserver</code> when starting a new TurboVNC session</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        The TurboVNC Session Manager will pass these command-line arguments to 
        the <code>vncserver</code> script when starting a new TurboVNC session 
        on the TurboVNC host.  This can be used, for instance, to enable 
        <a href="#ALR">automatic lossless refresh</a><a name="idx0035"></a>.
    </dd>
</dl>

<p><a name="TVNC_SERVERDIR"></a></p>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_SERVERDIR</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.serverdir</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">The directory in which the TurboVNC Server is installed on the TurboVNC host</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard"><code>/opt/TurboVNC</code></td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        The TurboVNC Session Manager will execute <code>bin/vncserver</code> and 
        <code>bin/vncpasswd</code> from this directory on the TurboVNC host.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.sessmgr = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable the TurboVNC Session Manager</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Enabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        Disabling this property will completely disable the TurboVNC Session 
        Manager.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>TVNC_SINGLESCREEN = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.singlescreen = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable forcing a single-screen layout when using automatic desktop resizing</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        The default behavior of the TurboVNC Viewer, when automatic desktop 
        resizing is enabled, is to request a desktop size from the server that 
        will fit within the viewer window without using scrollbars, and (if 
        multi-screen spanning is enabled) to request a screen layout from the 
        server that will align the server&rsquo;s screen boundaries with the 
        client&rsquo;s when the viewer window is in its default position.  
        Setting this environment variable or property to 1 will restore the 
        automatic desktop resizing behavior of previous versions of the TurboVNC 
        Viewer, thus forcing the server to use a single-screen layout even if it 
        supports multi-screen layouts.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.sshauth</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Preferred authentication methods for the built-in SSH client</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard"><code>publickey,keyboard-interactive,password</code></td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        This system property can be used to enable or disable particular SSH 
        authentication methods, as well as to specify their preferred order.  
        The same thing can be accomplished by using the 
        <code>PreferredAuthentications</code> directive in the OpenSSH config 
        file.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.sshbannerdlg = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Display the banner message from the SSH server in a dialog box</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        The default behavior of the TurboVNC Viewer is to display the banner 
        message from the SSH server on the command line.  Enabling this system 
        property causes the viewer to display the banner message in a dialog box 
        instead.
    </dd>
</dl>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.swingdb = <em>0 | 1</em></code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">Disable/enable Swing double buffering</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">Disabled</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        The TurboVNC Viewer has its own double buffering mechanism, so it 
        normally disables the double buffering mechanism in Swing and Java 2D in 
        order to increase performance.  This also allows the viewer to achieve 
        optimal performance under X11 without requiring MIT-SHM pixmap support. 
        Although the viewer has been thoroughly tested, the 
        <code>turbovnc.swingdb</code> system property is provided as a fallback 
        in case issues are discovered when running it under a specific version 
        of Java.
    </dd>
</dl>

<p><a name="VNC_VIA_CMD"></a></p>

<div class="table">
<table class="standard">
  <tr class="standard">
    <td class="high standard">Environment Variable</td>
    <td class="standard"><code>VNC_VIA_CMD</code>, <code>VNC_TUNNEL_CMD</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Java System Property</td>
    <td class="standard"><code>turbovnc.via</code>, <code>turbovnc.tunnel</code></td>
  </tr>
  <tr class="standard">
    <td class="high standard">Summary</td>
    <td class="standard">SSH command-line templates for use with the <code>via</code> and <code>tunnel</code> options (respectively)</td>
  </tr>
  <tr class="standard">
    <td class="high standard">Default Value</td>
    <td class="standard">See below</td>
  </tr>
</table>
</div>


<dl class="Description">
    <dt class="Description-1 Description">Description</dt>
    <dd class="Description-1 Description">
        When the <code>-via</code> option is used along with the 
        <code>-extssh</code> option, the TurboVNC Viewer reads the 
        <code>VNC_VIA_CMD</code> environment variable or the 
        <code>turbovnc.via</code> system property, expands patterns beginning 
        with the &ldquo;%&rdquo; character, and uses the resulting command line 
        to establish the secure tunnel to the VNC gateway.  If 
        <code>VNC_VIA_CMD</code> is not set, then this command line defaults to  
        <code>/usr/bin/ssh&nbsp;-f&nbsp;-L&nbsp;%L:%H:%R&nbsp;%G&nbsp;sleep&nbsp;20</code> 
        on Linux/Un*x and Mac systems and 
        <code>ssh.exe&nbsp;-f&nbsp;-L&nbsp;%L:%H:%R&nbsp;%G&nbsp;sleep&nbsp;20</code> 
        on Windows systems. <br /><br /> When the <code>-tunnel</code> option is 
        used along with the <code>-extssh</code> option, the TurboVNC Viewer 
        reads the <code>VNC_TUNNEL_CMD</code> environment variable or the 
        <code>turbovnc.tunnel</code> system property, expands patterns beginning 
        with the &ldquo;%&rdquo; character, and uses the resulting command line 
        to establish the secure tunnel to the VNC host.  If 
        <code>VNC_TUNNEL_CMD</code> is not set, then this command line defaults 
        to 
        <code>/usr/bin/ssh&nbsp;-f&nbsp;-L&nbsp;%L:localhost:%R&nbsp;%H&nbsp;sleep&nbsp;20</code> 
        on Linux/Un*x and Mac systems and 
        <code>ssh.exe&nbsp;-f&nbsp;-L&nbsp;%L:localhost:%R&nbsp;%H&nbsp;sleep&nbsp;20</code> 
        on Windows systems. <br /><br /> The following patterns are recognized 
        in the <code>VNC_VIA_CMD</code> and <code>VNC_TUNNEL_CMD</code> 
        environment variables and their corresponding system properties (note 
        that <code>%H</code>, <code>%L</code> and <code>%R</code> must be 
        present in the command template, and <code>%G</code> must also be 
        present if using the <code>-via</code> option): <br /><br />
        <div class="table">
        <table class="standard">
          <tr class="standard">
            <td class="standard"><code>%%</code></td>
            <td class="standard">A literal &ldquo;%&rdquo;</td>
          </tr>
          <tr class="standard">
            <td class="standard"><code>%G</code></td>
            <td class="standard">gateway host name or IP address</td>
          </tr>
          <tr class="standard">
            <td class="standard"><code>%H</code></td>
            <td class="standard">remote VNC host name or IP address (if using the <code>-via</code> option, then this is specified from the point of view of the gateway)</td>
          </tr>
          <tr class="standard">
            <td class="standard"><code>%L</code></td>
            <td class="standard">local TCP port number</td>
          </tr>
          <tr class="standard">
            <td class="standard"><code>%R</code></td>
            <td class="standard">remote TCP port number</td>
          </tr>
        </table>
        </div>
        
    </dd>
</dl>

<p><br /></p>


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